An explosion ripped through the international arrivals hall at the busiest airport in Moscow yesterday, killing 35 people and wounding about 130.
The state RIA Novosti news agency, citing law enforcement sources, said the afternoon explosion at Domodedovo Airport might have been caused by a suicide bomber.
"From the preliminary information we have, it was a terror attack," President Dmitry Medvedev told officials in a televised briefing.
Mr Medvedev ordered authorities to beef up security at Moscow's two other commercial airports and other key transport facilities, including the subway system, the target of past terror attacks. He said the explosion demonstrated that security regulations had been breached.
Mr Medvedev postponed his planned departure for the World Economic Forum in Davos, Switzerland, where he was to give the opening address tomorrow.
Prime Minister Vladimir Putin's United Russia party called the attack a "terrible tragedy" and called for the perpetrators to be "found and mercilessly punished".
Matthew Clements, an analyst for IHS Jane's, a global intelligence consultancy, said: "The attack is almost certainly the work of Islamist militants operating out of Russia's North Caucasus region.
"Militants in the area have increased the tempo and scale of their attacks over the past three years, operating under the loose banner of the North Caucasus Emirate, a jihadist group calling for the creation of an Islamic caliphate across the North Caucasus."
Built in 1964, Domodedovo is 42 kilometres south-east of Moscow and is the largest of the three major airports that serve the Russian capital, handling more than 22 million travellers last year.
Although there have been repeated attacks on the Moscow subway and on Russian trains - most blamed on Chechen militants - the bombing yesterday was the first involving a Russian airport since 2004.
Sergei Lavochkin, who was waiting in the arrivals hall for a friend to arrive from Cuba, said he saw emergency teams carrying bloodied people out of the terminal.
"I heard a loud bang, saw plastic panels falling down from the ceiling and heard people screaming. Then people started running away," Mr Lavochkin told Rossiya 24 television.
Mark Green, a British Airways passenger who had just arrived at the airport, told BBC television he heard a huge explosion as he left the terminal.
"Literally, it shook you," he said. "As we were putting the bags in the car a lot of alarms … were going off and people started flowing out of the terminal, some of whom were covered in blood.
"One gentleman had a pair of jeans on that was ripped and his thigh from his groin to his knee was covered in blood."
Mr Green said thousands of people were in the terminal at the time of the blast.
Alexei Spiridonov, who works for a car rental company at the airport, told Bloomberg News Service he saw the explosion. About 20 people were carried out on baggage carts, he said."There was a fairly loud bang, after which I saw smoke. There was a burning smell and people began to run away."
The German foreign minister, Guido Westerwelle, said he learnt "with consternation" of the attack. "I condemn this cruel bloody deed in the strongest terms," he said.
"This barbaric act is in no way justifiable."
The Nato secretary general, Anders Fogh Rasmussen, said he was "deeply disturbed" by the reported terror attacks.
"I strongly condemn it," he said on Twitter. "Nato and Russia stand together in the fight against terrorism."
In 2004, two suicide bombers were able to board planes at Domodedovo by buying tickets illegally from airport personnel. The female bombers blew themselves up in mid-air, killing all 90 people aboard the two flights.
Currently, 77 airlines offer regular flights to Domodedovo, serving 241 international and national routes, according to the airport's website.
The airport insists that security is one of its top priorities, claiming on its website that its "cutting-edge operations technology guarantees the safety of passengers' and guests' lives".
* With additional reporting by the Associated Press and Bloomberg