A website used by Russia's North Caucasus rebels on Sunday denied any link to the deadly Boston Marathon bombings that have been blamed on two ethnic-Chechen suspects.
"The command of the Vilayat Dagestan mujahedeen... declares that the Caucasus fighters are not waging any military activities against the United States of America," the Kavkacenter.com website said.
"We are only fighting Russia, which is not only responsible for the occupation of the Caucasus, but also for monstrous crimes against Muslims," the rebel site said.
US media reports said the FBI was studying possible links between the two suspects -- brothers Dzhokhar and Tamerlan Tsarnaev -- to the Caucasus Emirate movement led by feared warlord Doku Umarov.
The reports said the US authorities were particularly interested in the Vilayat Dagestan offshoot of Umarov's group.
Dagestan is a neighbouring republic of Chechnya with a large ethnic Chechen minority.
It has also been one of the most violent regions of Russia since the second of two post-Soviet era wars ended in Chechnya about a decade ago.
The Russian authorities said they were also checking the brothers' links to the rebels but had been unable to find any evidence so far.
"At the moment, we have no credible information about the Tsarnaev brothers' involvement with the Caucasus Emirate movement," an unnamed Russian security source told the Interfax news agency.