Jan. 19, 2014 -- Citing a new "surprise package" for Russia and Olympic spectators, Islamist militants in the North Caucasus Sunday launched a new threat to the Sochi Olympics with a purported "martyrdom" video by two suicide bombers who attacked a transit hub 400 miles away.

The video posted on a Chechen extremist site considered a credible platform for militant statements featured two unidentified men before the black flag of jihad and cradling AKMS rifles.

The duo -- dressed in street clothes and without the usual trappings of jihadis -- casually explained that Russians and those attending the Winter Games next month will not be safe as long as forces sent by President Vladimir Putin occupy the North Caucasus region near Sochi, Russia.

"We'll have a surprise package for you," one of the men said in the militants' video. "And those tourists that will come to you, for them, too, we have a surprise. If it happens [the Olympics], we'll have a surprise for you. This is for all the Muslim blood that is shed every day around the world, be it in Afghanistan, Somalia, Syria, all around the world. This will be our revenge."

The new video posted online overnight showed news and security camera footage of two suicide bomb blasts late last month at a busy train station and a commuter trolley in the city of Volgograd, which is a major transit hub in Russia.

U.S. officials said they are studying the video.

The video comes one day before the Olympic torch relay is scheduled to go through Volgograd Monday.

U.S. intelligence officials consider the threats from the Islamic terror groups against the Olympics to be very serious, which helped lead to the unusually strong travel advisory issued by the State Department this week for Americans who plan to travel to Sochi for the Olympics.

"I think the threats are real. [Islamist Chechen leader Doku] Umarov basically called for attacks on the Olympics," House Homeland Security Committee Chairman Rep. Mike McCaul, R-Texas, told ABC News' "This Week" today. "I think you're going to see attempts to do that. I think it's more likely that the attacks will happen outside the perimeter, more soft targets, transportation nodes."

ANALYSIS: Sochi 2014 Olympics in Terrorists' Crosshairs

A secret contingency operation is underway by the U.S. government to prepare for responding to a terrorist attack in Sochi and evacuating athletes and dignitaries, ABC News intelligence sources said.

U.S. officials continue to say the Russians are not fully cooperating with American security forces, at least as much as the Americans would like.

There will be small armed teams of U.S. security personnel allowed to be in Sochi, but the Russians are very much running their own show, in their own way, and apparently don't see any need to let U.S. security personnel in on every plan or piece of intelligence. U.S. officials said they are concerned that if they complain too much, the Russians could restrict even more the number of armed U.S. personnel allowed to be in the country.

This report has been updated to reflect that Rep. Michael McCaul is the Chairman of the House Homeland Security Committee, not the House Intelligence Committee as originally reported.

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