WASHINGTON — Tensions rose Sunday over security preparations ahead of the Winter Olympics in Sochi, as several congressional leaders expressed concern about Russia’s willingness to share information about terrorist threats, while President Vladimir V. Putin asserted that he would “do whatever it takes” to protect the thousands of visitors arriving soon for the Games.

The separate remarks, made on Sunday morning news programs, came before a video was released online showing two young men who said they were behind suicide bombings in the central Russian city Volgograd last month that claimed 34 lives. In the video, the men threaten to carry out more attacks. In a statement posted with the video on its website, the militant group Vilayat Dagestan claimed responsibility for the Volgograd bombings, The Associated Press reported.

Extremists affiliated with Doku Umarov, a former Chechen nationalist leader who now heads a broad Muslim separatist movement and advocates global jihad, have also vowed to disrupt the Games.

Representative Mike Rogers, Republican of Michigan and the chairman of the House Intelligence Committee, said Sunday that American officials working with Russians ahead of the Games had “found a departure of cooperation that is very concerning.”