US Defense Secretary Chuck Hagel called his Russian counterpart Sergey Shoygu and promised security assistance for the Winter Olympics in Sochi.
"Secretary Hagel offered his condolences for the recent terrorist attacks in Volgograd," Xinhua reported Saturday citing Pentagon spokesman John Kirby's statement.
"The secretary condemned the attacks and said the United States stands with the Russian people against terrorism," the statement said.
"Secretary Hagel also assured Minister Shoygu that the United States stands ready to provide security assistance to Russia for the Winter Olympics in Sochi, if requested," Kirby said.
The two defense chiefs also discussed the international efforts to remove Syria's chemical weapons stockpile, he added.
Two suicide bombings hit Volgograd, the first at a railway station Dec 29, 2013 and the other aboard a trolley bus Dec 30, 2013, leaving at least 34 people dead and scores of others wounded.
The attacks have raised questions about security of the upcoming Winter Olympics to be held Feb 6-23 in Sochi, Russia.