Smoke billows from the Zaventem Airport after a controlled explosion in Brussels, Tuesday, March 22, 2016. Bombs struck the Brussels airport and one of the city's metro stations Tuesday, killing and wounding dozens of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Michel Spingler)
People walk away from the broken windows at Zaventem Airport in Brussels after an explosion on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
A woman is evacuated in an ambulance by emergency services after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)
French police officers patrol outside the Gare du Nord train station, where high speed trains depart to Brussels, in Paris, Tuesday, March 22, 2016. Authorities in Europe and across the world tightened security at airports, railway stations, government buildings and other key points after deadly attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Francois Mori)
People stand near Brussels airport after being evacuated following explosions that rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing a number of people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)
Hooded Belgian police officers patrol outside the Gare du Midi train station in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Michel Spingler)
Police patrol the EU commission building, after a bomb exploded nearby, at the subway in Brussels, Belgium, Tuesday, March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing a number of people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Martin Meissner)
A Eurostar representative gives advice to a traveler after services were suspended on the Brussels Eurostar train route because of the attacks in Belgium, at St Pancras international railway station in London, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Matt Dunham)
In this photo provided by Georgian Public Broadcaster and photographed by Ketevan Kardava a man speaks on a mobile phone in Brussels Airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. A developing situation left a number dead in explosions that ripped through the departure hall at Brussels airport Tuesday, police said. All flights were canceled, arriving planes were being diverted and Belgium's terror alert level was raised to maximum, officials said. (Ketevan Kardava/ Georgian Public Broadcaster via AP)
People are evacuated from Zaventem Airport in Brussels after an explosion on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)
People react outside Brussels airport after explosions rocked the facility in Brussels, Belgium, on Tuesday, March 22, 2016. Explosions at the airport and at a subway station killed at least 31 people and injured more than 100. (AP Photo/Geert Vanden Wijngaert)
This photo provided by Georgian Public Broadcaster and photographed by Ketevan Kardava, shows the scene in Brussels Airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. A developing situation left a number dead in explosions that ripped through the departure hall at Brussels airport Tuesday, police said. All flights were canceled, arriving planes were being diverted and Belgium's terror alert level was raised to maximum, officials said. (Ketevan Kardava/ Georgian Public Broadcaster via AP)
Emergency services evacuate a victim wrapped in a blanket after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)
People react outside Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)
Emergency services after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Sylvan Plazy)
A truck carrying soldiers of the Belgian Army arrives after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)
A family look out of the window of a bus after being evacuated from Brussels airport, after explosions rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing at least 13 people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)
In this image made from video, emergency rescue workers stretcher an unidentified person at the site of an explosion at a metro station in Brussels, Belgium, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said.(APTN via AP)
People react as they walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)
People react as they walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)
People react as they walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)
In this photo provided by Georgian Public Broadcaster and photographed by Ketevan Kardava two women wounded in Brussels Airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. A developing situation left at least one person and possibly more dead in explosions that ripped through the departure hall at Brussels airport Tuesday, police said. All flights were canceled, arriving planes were being diverted and Belgium's terror alert level was raised to maximum, officials said. (Ketevan Kardava/ Georgian Public Broadcaster via AP)
In this photo provided by Georgian Public Broadcaster and photographed by Ketevan Kardava a man is wounded in Brussels Airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. A developing situation left at least one person and possibly more dead in explosions that ripped through the departure hall at Brussels airport Tuesday, police said. All flights were canceled, arriving planes were being diverted and Belgium's terror alert level was raised to maximum, officials said. (Ketevan Kardava/ Georgian Public Broadcaster via AP)
People walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)
In this image provided by Daniela Schwarzer, smoke is seen at Brussels airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. (Daniela Schwarzer via AP)