WASHINGTON (AFP) - Investigators are pursuing other "persons of interest" possibly linked to the deadly Boston Marathon bombings, US lawmakers said on Sunday.

"There are still persons of interest in the United States that the FBI would like to have conversations with," House Intelligence Committee Chairman Mike Rogers told ABC's This Week. The Michigan Republican declined to indicate how many such people were on the radar of authorities.

Dutch Ruppersberger, the top Democrat on the panel, said investigators were scouring telephone logs that took place before and after the April 15 twin blasts that killed three people and wounded more than 260.

Authorities have identified two brothers - Tamerlan and Dzokhar Tsarnaev - as the suspects. Tamerlan died during a shootout with police days after the attacks, but his 19-year-old brother was captured alive and is being held at a federal prison medical center outside Boston.

Representative Michael McCaul, head of the House Homeland Security Committee, said the suspects likely got training from violent extremists, considering the "level of sophistication" of the device used for the attack.

Investigators are said to believe the Tsarnaevs' pressure-cooker bombs were likely detonated by long-range remote controls.

Mr McCaul also stressed that pressure-cooker bombs were a "signature device" used in Pakistan and Afghanistan.

In addition, "the way they handled these devices and the trade craft leads me to believe that there was a trainer," he said on Fox News Sunday.

"And the question is, where is that trainer or trainers? Are they overseas in the Chechen region or are they in the United States?" The lawmakers' comments came as US media reported that Russian authorities secretly wiretapped the mother of the brothers, Zubeidat Tsarnaeva, and recorded her discussing jihad in vague terms during a 2011 telephone conversation with Tamerlan.

Even though the conversation took place two years ago, the Russians only turned over the information to their US counterparts in recent days, according to the reports.

The investigation has also focused on a mysterious man named Misha who is said to have influenced Tamerlan and possibly encouraged him to go down a radical path.

Both the CIA and the FBI flagged Tamerlan over possible terror ties after Russian officials contacted the US agencies in 2011.

Reports said Russian authorities had also alerted their US counterparts about concerns that his mother was a religious extremist, and that she was added along with her older son to a terror watchlist.

Still, Rogers said Moscow has more information that would be "incredibly helpful." "There's a cultural problem there between where the Russians are and our folks," he said. "I believe that they have information, and had more information."

Democratic Representative Adam Schiff claimed the Russians were not disclosing everything they know - especially in regards to the mother.

"There's got to be a basis for why they went up on her electronically or why they went up on one of her affiliates or associates," he said on CNN's State of the Union. "We don't know that. We haven't received that information from the Russians," he added. "I think they do know more than they're telling us."

Attention also turned to why US authorities failed to connect the dots and prevent the attacks - considering what they knew at the time, and in the wake of the lessons thought to have been learned from the intelligence failures leading up to the Sept 11, 2001 attacks.

Republican Senator Lindsey Graham, for one, told CBS's Face The Nation that "we're going to have to up our game."

"It's a failure to share information and missing obvious warning signs," he said.