Islamist rebels in the Russian republic of Dagestan have denied any links to the bombing of the Boston marathon.
US investigators have begun to focus on a trip last year to Dagestan taken by Tamerlan Tsarnaev, the suspect killed during a manhunt on Friday, to see if he developed ties with the restive republic's violent rebel movement, the Vilayat Dagestan.
"The Vilayat Dagestan command ... indicates that mujahideen from the Caucasus are not at war with the United States of America," the group said in a statement.
"We are at war with Russia, which is responsible not only for the occupation of the Caucasus, but also of heinous crimes against Muslims."
Dagestani rebels, under the Caucasus Emirate umbrella group seeking to create an Islamist state along Russia's southern and mainly Muslim flank, have terrorised the republic for years.
They organise training camps and safe houses, but have focused their attacks on security officials and religious figures who collaborate with the state.
Sniper attacks are a regular occurrence. On Sunday, a homemade bomb exploded near a police officer's car but did not cause any injuries.
The statement also said the group followed an order issued by Doku Umarov, head of the Caucasus Emirate and Russia's enemy No1, to avoid attacks on civilians.
The statement added: "If US authorities are really interested in establishing the true organisers of the explosions in Boston, and not co-operating with Russian speculation, then they should focus on the Russian special services involvement in the events."
Russia has failed to put down its Islamist insurgency, originating from the separatist wars in Chechnya that erupted after the fall of the Soviet Union.
Tsarnaev and his younger brother Dzhokhar, who is currently in US detention, sympathised with the Chechen independence movement, according to social media accounts. The two reportedly never lived in Chechnya, torn apart by war for much of the 1990s, but stayed in neighbouring Dagestan for six months before moving to the United States in 2002.
Their parents moved back to Dagestan a couple of years ago and remain in the republic's capital, Makhachkala.
Relatives have suggested that the older Tsarnaev had become radicalised in the US, before he took his trip to Russia in the first half of last year. On that trip, he visited his father in Dagestan as well as visiting Chechnya.
The FBI repeatedly questioned Tsarnaev in 2011. That prompted the Department of Homeland Security to deny his September 5 application for US citizenship, The New York Times reported yesterday. The younger Tsarnaev, 19, had his citizenship application approved.
"We checked all the channels of information for possible links between the Tsarnaevs and Umarov, but found no facts to confirm that link," a source told RIA-Novosti, a state-owned news agency, on Sunday.
"If the Tsarnaevs had been linked to Umarov's bandit group then their names would have been in the security services database. We don't have such last names [in it]," the source said.