MOSCOW -- A U.S. congressional delegation is spending a week in Russia meeting with high-level government and security officials to investigate whether more could have been done to prevent the Boston Marathon bombings.

Russia warned the United States in 2011 that bombings suspect Tamerlan Tsarnaev was a potential terrorist threat, but did not respond to U.S. requests for more information.

"We think there is some information that is vital for us to know that hasn't been made public yet," Rep. Dana Rohrabacher, the California Republican who is leading the delegation, said Wednesday after the congressmen laid a wreath at the site of a 2000 terrorist attack in Moscow.

The delegation includes Rep. Michele Bachmann, who announced early Wednesday she wouldn't run for re-election in 2014. She was scheduled to arrive in Moscow late Wednesday, a day after the rest of the delegation.

Tsarnaev, who was killed by police a few days after the April 15 attack in Boston, spent six months last year in Dagestan, a southern Russian province that is the centre of a low-level Islamic insurgency. U.S. investigators are trying to determine whether Tsarnaev was radicalized during his time there.

Tsarnaev has ethnic roots and relatives in Dagestan and also in neighbouring Chechnya, where federal troops and separatist militants fought two devastating wars in the past two decades. The wars spawned the Islamic insurgency that has spread throughout Russia's Caucasus.

Politico reported Tuesday that the congressional delegation had originally planned to visit Chechnya with help from action movie star Steven Seagal, but then reconsidered.

Seagal, who met with President Vladimir Putin in March, visited Chechnya's strongman leader Ramzan Kadyrov last week. Kadyrov's spokesman posted a picture of Seagal on Instagram and quoted him as saying that he would return this week with the congressional delegation.

Rohrabacher confirmed to The Associated Press that the delegation had been in touch with Seagal, but declined to comment further.

Kadyrov often boasts of his success in quashing terrorism, but rights activists accuse him and his feared security forces of staggering abuses, including abduction, torture and murder.

Although the U.S. and Russian presidents have pledged to improve counterterrorism co-operation, both sides have accused the other of being less than forthcoming. U.S. officials have expressed frustration with the lack of information provided by Russia.

Russia's security services this month said they had caught a U.S. Embassy employee in a clumsy attempt to recruit a Russian counterterrorism officer specializing in Dagestan. Russia accused the American of working for the CIA and expelled him.

In addition to Bachmann and Rohrabacher, who is chairman of the U.S. House Foreign Affairs Committee's Subcommittee on Europe, Eurasia and Emerging Threats, the congressional delegation includes William Keating, Steve King, Paul Cook and Steven Cohen.