In a telegram to Russian President Dmitry Medvedev, the Pope spoke of his “profound pain and firm condemnation” of the attack and “his feelings of spiritual closeness and heartfelt condolences to the victims’ families.”
A 39-year-old British man was among those killed in the suicide attack on Domededovo Airport. Property consultant Gordon Cousland, who has a six-month-old daughter, was due to marry in the spring.
Russian Prime Minister Vladimir Putin has vowed to root out those behind the attack, believed to be Islamic militants from the North Caucasus region.
“Everything must be done to find, expose and bring the bandits who committed this crime to court – and the nests of these bandits, however deep they have dug in, must be liquidated,” he said.
Patriarch Kirill of Moscow and All Russia conducted a religious service in Moscow on Tuesday for all those who died in the explosion.
According to Interfax news agency, the Russian Orthodox leader called upon Russians to unite in the wake of the "horrific" attack.
"There is and there can be no justification for such criminal aggression," he said in a statement.
The people of Russia must now "unite to fight against inhumane attacks that kill innocent people."
"The people who committed this have put themselves outside law, both human and divine," he said.
Pavel Tokarchuk, director of Russian Ministries’ Moscow office, has asked for prayers in a message to supporters on the ministry’s website.
He wrote: “I was there [at Domodedovo] a week ago flying through to Siberia on a Project Hope trip. Very crowded airport. What has happened is just unbearable.
"Please, raise your prayers for the relatives of the victims, and for the more than 50 people who are in the critical conditions because of their injuries.”