Rebels in the North Caucasus region issued a statement on Sunday saying that they are not at war with Washington and have no link to the April 15 bombing of the Boston Marathon that killed three people and injured about 180.
"The Caucasian Mujahedeen are not fighting with the United States of America," according to the statement on Kavkazcenter.com, which was attributed to unidentified Mujahedeen commanders in Dagestan.
"We are at war with Russia, which is responsible not only for the occupation of the Caucasus, but also for heinous crimes against Muslims."
The two suspects in the bombing, Tamerlan Tsarnaev, 26, who was killed in a gunfight with police and Djokhar, 19, who is in police custody, are ethnic Chechen brothers.
Media reports in the United States said the FBI was studying possible links between the Tsarnaev brothers and the Caucasus Emirate movement led by feared warlord Doku Umarov.
US authorities were said to be particularly interested in the Vilayat Dagestan offshoot of Umarov's group.
Dagestan is a neighboring republic of Chechnya with a large ethnic Chechen minority.
It has 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.
Russian authorities said they were also checking the siblings' links to the fighters 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.
Russia asked the FBI to investigate the older Tsarnaev brother in 2011 over concerns he might be linked to terrorist groups. The FBI interviewed Tsarnaev and his family and conducted a search but did not find anything suspicious.
Last year, Tsarnaev spent six months in the volatile region around Chechnya and neighboring Dagestan.
The Kavkazcenter.com website statement called on the US media to stop linking the region with the attacks on Boston.
"If the US authorities really are interested in finding the true organizers of the Boston bombings... they should start focusing on the involvement of the Russian secret services," said the rebel site.
AFP contributed to this report.