Russian officials notified U.S. intelligence multiple times over concerns regarding bombing suspect Tamerlan Tsarnaev, according to reports in Russia.

As Boston continues to remember those who lost their lives in the marathon bombings, questions are being raised over just how much was known about the suspects.

Reports suggest Russia tipped off U.S. intelligence officials "several" times about Tamerlan Tsarnaev, the older brother of the two suspects who was killed in the ensuing manhunt.

A report in the Boston Globe says one of these alerts came after Tamerlan was first investigated by the FBI.

U.S. officials also say the bureau was alerted when he travelled to Russia last year.

As some on Capitol Hill question how information was handled, a White House spokesman says investigations were properly conducted.

Police say Tamerlan and his brother Dzhokhar planted bombs at the marathon, killing three people and injuring hundreds.

Officials believe they may have been radicalised by anti-U.S. information on the internet.