国际英语新闻：Explosion at Moscow's airport kills at least 31

"According to intelligence, three men may have been involved in organizing the explosion. They have been living in the region of the Russian capital for some time," the source was quoted by Interfax as saying.

A source said the blast was equivalent to 5-10 kg of TNT.

Eyewitnesses said there was a heavy smoke at the airport and the entry from the arrivals zone has been closed.

After the blast, Moscow's Sheremetyevo Airport is accepting planes that were bound for Domodedovo.

Moscow police has tightened the security in the city's other airports and metro system.

Russian President Dmitry Medvedev, who called this blast a terrorist attack, is holding an urgent meeting and ordered measures to ensure security at all Russian airports and transport facilities.

Medvedev has decided to cancel his trip to the annual World Economic Forum in Switzerland's Davos after the deadly blast, RIA Novosti news agency reported.

Domodedovo is Moscow's most updated and busiest airport. In 2004, two planes which took off from the airport were blown up by female Chechen suicide bombers, killing a total of 90 people on board.