Investigators are pursuing other "persons of interest" who may be linked to the deadly bombings at the Boston Marathon, a US lawmaker said on Sunday.

"There are still persons of interest in the United States that the FBI would like to have conversations with," Congressman Mike Rogers, Republican chairman of the House Intelligence Committee, told ABC's "This Week." He declined to provide a number.

Authorities have identified two brothers -- Tamerlan and Dzokhar Tsarnaev -- as the suspects in the April 15 twin bombings at the Boston Marathon that killed three people and wounded more than 260 others.

While Tamerlan was killed during a shootout with police days after the attacks, his 19-year-old brother Dzhokhar was captured alive and is being held at a federal prison medical center.

Rogers' comment came as US media reported that Russian authorities secretly wiretapped the mother of the brothers and recorded her discussing jihad in vague terms during a 2011 telephone conversation.

The Russians only turned over the information to their US counterparts in recent days, according to CNN.

A US official with knowledge of the investigation who confirmed the intercept to the US television network declined to confirm who was on the other line.

Asked about the report late Saturday, Attorney General Eric Holder declined to comment, saying it was an "ongoing matter."

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, Zubeidat Tsarnaeva, was a religious extremist, and that she was added along with her older son to a terror watchlist.