The FBI interviewed the parents of the Boston bombing suspects in the Russian Republic of Dagestan on Tuesday with the help of Russian authorities.
The parents of Tamerlan and Dzhokhar Tsarnaev are currently living in Dagestan, an overwhelmingly Muslim region on the Caspian Sea where the family briefly lived before leaving for the United States.
"The FBI is receiving cooperation from the Russian government in its investigation of the Boston marathon bombing," a US embassy official, speaking on condition of anonymity, told AFP.
"A group from the US Embassy in Moscow travelled to Dagestan yesterday (Tuesday) as part of this cooperation with the Russian government to interview the parents."
The official declined to say whether the delegation was still in Dagestan, but a security source told an AFP correspondent that interviews with both parents took place overnight and involved representatives of the FBI.
"The parents were taken home but in the morning the mother came back for more questioning," the source said.
The Dagestan security source also said the parents were asked by American officials about Tamerlan's visit to Dagestan. "The parents replied that he did not make contact with radical Islamists."
The two brothers, who had been living in the United States for over a decade, are accused of the twin marathon bombing on April 15, which killed three people and wounded more than 260 others.
Tamerlan, 26, was killed in a shootout with US police while Dzhokhar, 19, was gravely wounded during his capture last week. He remains hospitalized and has been read the charges of using and conspiring to use a weapon of mass destruction.
The brothers' father Anzor, an ethnic Chechen born in Kyrgyzstan, has repeatedly said in media interviews that his sons were innocent and could not have carried out the bombings.
According to the RIA Novosti news agency, both parents agreed during the questioning to travel to the United States to help with the investigation there.
"We plan on Thursday in the second half of the day to fly to the United States," Anzor Tsarnaev told RIA Novosti, without giving further details.