Russia has balked at sharing specific information on terror threats made against the Sochi Olympics with Washington, a US official said amid mounting fears over security at the Games. The Obama administration meanwhile publicly stopped short of expressing full confidence in a massive Russian security operation ahead of the sporting spectacular opening next month in the Black Sea resort and nearby mountains. Signs of increasing US concern followed a telephone discussion on security at the Sochi Olympics between Presidents Barack Obama and Vladimir Putin on Tuesday. A senior US official told AFP on condition of anonymity that Russia "has not been forthcoming in sharing specific threat information." Extremist insurgents based in North Caucasus republics such as Dagestan who are seeking their own independent state have vowed to disrupt the Sochi Games in an effort to undermine Putin. Washington, which has sophisticated intelligence and counterterrorism capabilities that have been deployed in previous Olympics, has offered Russia security assistance as it places a ring of steel around the host city and venues shortly to welcome thousands of athletes and spectators. White House spokesman Jay Carney admitted earlier that there was "concern" in Washington about an uptick in reporting of threats by Islamic extremists relating to the Sochi Games. He said the United States would send diplomatic security and FBI agents who would liaise with Russian security officials to protect American athletes and spectators. But he did not take several opportunities offered by journalists to express full confidence in Russia's preparations. "I wouldn't be qualified or wouldn't want to venture to assess overall," Carney said. "These kinds of major events around the world obviously present security challenges," he said, without confirming whether Russia had accepted US offers of help. "The president spoke with President Putin about this. We have offered any assistance that they might want to avail themselves of." At the State Department, deputy spokeswoman Marie Harf deflected a query as to whether the United States had full confidence in the Russian effort, but added that Washington knew Moscow was "committed to doing everything they can in terms of security." The careful public tone adopted by the administration could signal a desire to avoid offending or antagonizing Russia in the run-up to the Games while concerns are expressed privately with top Russian officials. The Games are seen as hugely important to Putin's personal prestige and to his project of restoring stability and honor to Russia as it emerges from the post-Cold War period that saw the collapse of the Soviet Union. Ties between Moscow and Washington are currently as tense as they have been for many years, with the case of fugitive US intelligence leader Edward Snowden -- granted temporary asylum by Russia -- and the Kremlin's support for Syrian President Bashar al-Assad, fraying tempers. The call between Putin and Obama came amid signs of subtle but rising pressure on Russia over securing the Games from Washington. On Monday, the Pentagon said it was ready to deploy air and naval assets -- including two ships -- to help secure the Olympics, which begin on February 7. US Defense Secretary Chuck Hagel had already offered American support during a January 4 phone call with his Russian counterpart Sergei Shoigu. Security fears were exacerbated by two suicide bombings in the southern city of Volgograd last month -- Russia's deadliest in three years -- that killed 34 people. The State Department has warned Americans headed to Sochi to be vigilant. On Sunday, several prominent US lawmakers raised new concerns about Russia's security efforts to protect the Games, despite Moscow's effort to encircle the host city in a ring of steel. Michael McCaul, chairman of the House Homeland Security Committee, said there had been good cooperation between Russian authorities and the Federal Bureau of Investigation. But "it could be a lot better," he told ABC News in an interview from Moscow. Another Republican lawmaker, House Intelligence Committee Chairman Mike Rogers, said US officials were not getting all the information they needed to protect athletes at the Games. "What we're finding is they aren't giving us the full story about what are the threat streams, who do we need to worry about," he said. Source: AFP