A website used by Russia's North Caucasus rebels denied Sunday 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 Kavkazcenter.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.

Media reports in the United States said the FBI was studying possible links between the two main suspects -- brothers Dzhokhar and Tamerlan Tsarnaev -- and the Caucasus Emirate movement led by feared warlord Doku Umarov.

Monday's double bomb attack on the Boston Marathon killed three people and wounded about 180.

Dzhokhar, 19, is in serious condition in a Boston hospital following a massive manhunt on Friday in which Tamerlan, 26, was killed.

The media 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 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.

Much of the speculation has swirled around the role of the late Tamerlan, whose YouTube page has a playlist with links to men he identified as "terrorists" and Islamic preachers.

One link features a nearly hour-long speech by an Islamist named Sheik Feiz Mohammed, who intelligence sources in the US said had followers among the Dagestani guerrillas.

The Tsarnaev family has said that Tamerlan had visited Dagestan for six months last year.

One Russian report added that Tamerlan's father Anzor Tsarnaev had kicked his son out of his house because he began displaying radical Islamist ideology.

The younger brother Dzhokhar -- badly wounded by the time he was detained by authorities on Friday -- also identified Islam as a his "world view" on the VK social media site, the Russian equivalent of Facebook.

Dzhokhar also lists information about Chechnya and Islam as well as different mosques around the world.

Caucasus Emirates leader Umarov is widely recognised as Russia's public enemy number one who staged some of the deadliest bombings in Moscow and across the North Caucasus in the past five years.

He claimed responsibility for a Moscow airport attack in January 2011 that took 37 lives as well as earlier twin metro bombings in 2010 in which more than 40 people died.

But the Kavkazcenter.com website argued that Umarov never targeted foreigners and did not view them as a threat to his dream of establishing an Islamist state across the southern swathes of Russia.

"The command of the Vilayat Dagestan mujahedeen calls on the US media especially to stop their speculation and not to assist the Russian propoganda," Kavkazcenter.com said.

"If the US authorities really are interested in finding the true organisers of the Boston bombings... they should start focusing on the involvement of the Russian secret services," said the rebel site.