At least 35 people have been killed and 130 injured in an explosion at Moscow's Domodedovo International Airport.
A suicide bomber is believed to have been behind the attack, which took place at 4.32pm local time in an area close to the baggage reclaim area.
President Dmitry Medvedev vowed to track down and punish those behind the bombing, which also injured about 130 people during the busy late afternoon.
Speaking on Twitter Medvedev wrote 'security will be strengthened at large transport hubs, we mourn the victims of the terrorist attack at Domodedovo Airport. The organisers will be tracked down and punished.'
The Kremlin said Medvedev, who has called the insurgency in the north Caucasus the biggest threat to Russia's security, was delaying a trip to the Davos international business forum in Switzerland.
'According to preliminary information, the explosive device was set off by a suicide bomber,' Interfax news agency quoted an unnamed security source as saying.
Moscow police have stepped up security across the city after the blast.
Domodedovo Airport is Russia's largest airport in terms of passenger traffic.