Evgeny Khorishko of the Russian Embassy in Washington, D.C., told ABC News Monday it was "too early to say" who may have been responsible.
Initial reports published early Monday by Russia's state news agency RIA said witnesses had seen two suicide bombers carry out the attack. Later reports pointed to a single attacker. On Twitter, one purported eyewitness, Ilya Likhtenfeld, said the bomb was on a man standing in a crowd near a cafe.
U.S. President Barack Obama said he "strongly condemns this outrageous act of terrorism against the Russian people" and offered his condolences to those affected, according to a statement read today by White House press secretary Robert Gibbs. The U.S. State Department said it has no indication that any Americans were among those killed or injured.
Video taken inside the airport apparently minutes after the bombing shows the blast area full of smoke, with luggage scattered around the ground. Several bodies, prone and unmoving on the ground, are also visible.
No hard evidence has emerged yet to link the Domodedovo bombing to any specific terrorist group. However, according to counter-terrorism expert Richard Clarke, it fits the pattern of a persistent Chechen campaign of violence.
"This is part of a pattern where the Chechen rebel group attacks in Moscow or in Russia – a major attack about every two years," Clarke said Monday. "They've attacked in the metro, they've attacked in schools, they've attacked in apartment buildings… This is a regular pattern."
Suicide bombers, often female, from Chechnya or Dagestan and sometimes known as "black widows," have carried out many attacks on Russian targets in the past decade, including the simultaneous bombings of two planes mid-flight that killed 90 people in the summer of 2004 and a Moscow metro bombing that killed 10 a week later.
"Black widows" are often avenging the deaths of relatives at the hand of federal forces.
Last March, two female suicide bombers attacked the Moscow subway, killing 40 people and injuring more than 100.
Both women were from Dagestan in the restive North Caucasus region where Russian forces have been battling an Islamist insurgency. One was a 28-year-old schoolteacher, the other the 17-year-old widow of a local militant leader who was killed by Russian forces in 2009.
A Chechen militant leader, Doku Umarov, claimed he ordered the metro attack and warned of more attacks to come in a video posted online.
"Both of these operations were carried out on my command and will not be the last," Umarov said.
On Jan. 21, three days before the Domodedovo bombing, Russia's prime minister, Vladimir Putin said Russia must combat terrorism in the North Caucases by improving the quality of life for the people there.
"Our objective is to radically change the situation in the North Caucasus, primarily by improving the quality of life of the people, ensuring their security and giving them the opportunity to work and live in peace," Putin said. "We must eradicate the roots of terrorism and extremism, first of all poverty, unemployment, ignorance and inadequate levels of education, and corruption and lawlessness."
ABC News' Max Karmen contributed to this report.