At least 50 people were hospitalized, authorities said, and 35 were listed in critical condition.

Officials say the bombing was a terrorist attack and have called a "high terror alert" at Moscow's two other major airports and the metro system, where suicide bombers killed 40 people in March. There is heightened security throughout the city.

Interfax reported that police are seeking three men in connection with the bombing but did not provide details.

The blast detonated in a hall where arriving international passengers emerge from customs. Large crowds had gathered to await passengers as they departed the baggage area, police sources told the Interfax news agency. As at most airports, the area is outside the secure zone.

"Therefore, the bomb did not fly to Moscow by plane, it was brought in to the airport from outside," Interfax quoted the sources.

The explosion occurred at 4:37 p.m. local time, according to the Russian Air Transport Agency. Planes from Dusseldorf, Germany, and Odessa, Ukraine, had landed in the previous half-hour. Just before the blast, a plane from London had arrived.

An amateur video shot shortly after the blast showed bodies strewn about a smoke-filled hall. The lights were on, but workers with flashlights made their way through the smoke, amid luggage and several luggage carts.

Yelena Bakhtina, who works in a cafe at the other end of the hall, said on Russian television that she was about 100 yards from where the explosion took place when there was a sudden loud boom. She said the whole building shook, raining plaster down around her.

Sergei Lavochkin told Russian television's Channel One that he was at the airport waiting for a friend who was flying in from Cuba. "I was not that close to the place of the explosion, but I heard a strong noise and people's cries," he said, adding, "I saw people running away in panic. ... I saw two men sitting on the bench, their heads bleeding, and I saw men being carried on the luggage trolleys to the ambulances."

Another witness, Alexei Nefedov, told Russian television: "I saw a lot of smoke, a lot of police and a lot of firemen." He said passengers still in the customs area, which is behind a solid wall, were unhurt and continued to collect their luggage as it came off the carousels. As they began to emerge into the aftermath of the explosion, he said, they found a scene of destruction and death.

Russian President Dmitry Medvedev postponed his trip to the Davos World Economic Forum in Switzerland, where he had been scheduled to arrive Tuesday and to give the opening address on Wednesday. He appeared on Russian television in the late afternoon and expressed his condolences to the relatives of those killed, promising a full investigation of the bombing.

Medvedev, who after the explosion called a meeting with Transportation Minister Igor Levitin and Prosecutor General Yuri Chaika, criticized officials for not pursuing security precautions vigorously enough.

"What happened shows that not all laws are being correctly applied at various places," Medvedev said. "This has to be sorted out."

Domodedovo, on the southeast outskirts of Moscow, is Russia's biggest airport. It is used by United, Lufthansa, Austrian Air, British Airways and the Russian airline Transaero, among other airlines. It is also a hub for domestic travel. The United flight, from Washington, was not flying on Monday.

A spokesman for the U.S. Transportation Security Administration, said the TSA is monitoring the situation in Moscow. "We are working with our international partners to share information regarding the latest terrorist tactics and security best practices," Nick Kimball said. "Passengers may continue to notice unpredictable security measures in all areas of U.S. airports, including before the checkpoint."

The bombing was not causing any disruptions or changes to security at Washington's three major airports, according to spokesmen for the facilities.

Russian police said they believed that about 15 pounds of explosive had been used. Cellphone jamming devices were activated at the airport to try to prevent more potential bombs from being detonated.

Fifty ambulances were dispatched to Domodedovo, reports said.

By early evening, flights were being diverted to Vnukovo and Sheremetyevo airports.

Last month Moscow saw nearly a week of angry demonstrations by young Russian nationalists, provoked by the killing of a fan of the Spartak soccer team. They blamed migrants from the Caucasus, and there were several knifings in the city. Police had a difficult time containing the gatherings and detained dozens. They warned that people were coming to Moscow from the Caucasus to avenge the attacks by the nationalists, but it didn't happen.

Virtually all previous terrorist attacks in Russia have been carried out by separatists from Chechnya or elsewhere in the North Caucasus. This was apparently the first fatal explosion at an airport.

Last March in Moscow's metro, 40 people were killed and more than 70 were wounded when two bombs were detonated at two different stations, a half-hour apart. The blasts were triggered by two female suicide bombers, including the 17-year-old widow of an Islamist rebel leader. Doku Umarov, a Chechen militant, took responsibility for the bombings, which he called retaliation for an anti-terrorism raid in the North Caucasus by security forces in February in which at least 20 people were killed.

In 2004, female suicide bombers brought down two planes that had taken off from Domodedovo. They had apparently bribed their way on board.

Terrorists have also attacked gatherings with the aim of taking hostages - at a school in Beslan, in North Ossetia, in 2005, and at a theater in Moscow in 2002. Both ended with heavy casualties.

In 2000, apartment houses in Moscow were destroyed by bombs. Some suspected that the security services were behind those explosions, which led to a resumption of the war in Chechnya.

Domodedovo is Eastern Europe's busiest airport. Last year it handled 22.3 million passengers. Seventy-seven airlines schedule 600 flights a day there. It was thoroughly renovated in the late 1990s and overtook the dismal Sheremetyevo - for years Moscow's only international airport - as the city's most glamorous arrival point. Still, it requires a tedious drive through Moscow's vast southern regions, plus a 14-mile sprint through the suburbs, to get there.

Staff writer Ashley Halsey III contributed to this report.

englundw@washpost.com lallyk@washpost.com

www.washingtonpost.com/wp-dyn/content/article/2011/01/24/AR2011012401872_pf.html

Jan. 24, 2011