Russia on Friday called the deployment of U.S. troops in Jordan over the Syria crisis an unconstructive step that threatens to expand the conflict as the kingdom's Islamist opposition said Amman's government should review its decision.

U.S. Defense Secretary Chuck Hagel revealed Wednesday that 150 U.S. military specialists had been deployed in Jordan since last year and that he had ordered the army to bolster the mission by bringing the total American presence to more than 200 troops.

Russia said Wednesday it had destroyed nearly three-quarters of its world-topping stock of chemical weapons and expected to eliminate its entire arsenal by 2015 in line with a self-imposed deadline.

The United States has been concerned about Russia's ability or desire to eliminate the dangerous weapons -- pronounced illegal by a 1997 global convention -- after it tore up a reduction program agreement with Washington in 2012.

The twin blasts that killed three people and injured scores at the Boston marathon are a warning for Russia as it prepares to host the 2014 Winter Olympic Games, the sports minister said on Tuesday.

"For Russia, which will have to soon stage a number of major sporting events, this is a serious warning bell," RIA Novosti quoted Vitaly Mutko as saying.

Russia on Saturday published its own blacklist of U.S. officials banned from entering the country in retaliation for Washington blackballing 18 Russians over alleged human rights abuses.

Already-strained relations between the two countries chilled further as Russia hit back at what it called an "unfriendly" move by Washington that the foreign ministry warned would hurt mutual trust.

President Vladimir Putin on Friday unveiled a new $50 billion drive for Russia to preserve its status as a top space power, including the construction of a brand new cosmodrome from where humans will fly to space by the end of the decade.

Fifty-two years to the day since Yuri Gagarin became the Soviet Union's greatest hero by making the first human flight into space, Putin inspected the new Vostochny (Eastern) cosmodrome Russia is building in the Amur region of the Far East.

The Kremlin warned Washington on Friday against publishing a list of Russian officials barred from entering the United States because of their alleged abuse of human rights.

Russian media reports said the dozens of names included on the so-called "Magnitsky Act" -- named after Russian lawyer Sergei Magnitsky who died in prison after revealing a suspected state embezzlement scheme -- would be published in the United States later on Friday.

Russia on Wednesday vowed to extend economically struggling Serbia a $500-million loan while reasserting support for its ally's continuing refusal to recognize the independence of Kosovo.

Serbian Prime Minister Ivica Dacic won a promise of the quick disbursement of a $300-million (230-million-euro) loan that would help cover Belgrade's budget shortfall.

Russian Foreign Minister Sergei Lavrov warned Wednesday against heating up the North Korea crisis with military manoeuvres, but stressed that Moscow and Washington had a common stand.

"On North Korea we have no differences with the United States," he told journalists as he met with U.S. Secretary of State John Kerry for talks on the sidelines of a meeting of G8 foreign ministers in London.

Russia on Tuesday opened a legal case against top vote monitoring group Golos (Voice) after it failed to declare foreign funding and its status as "foreign agent" under a controversial new law.

The move comes as the authorities carry out a wide-ranging crackdown on NGOs that has included raids by prosecutors that sparked international concern.

The White House on Monday welcomed efforts by Russia and China to ease the crisis with North Korea, after pushing both nations to use their influence to change the isolated state's behavior.

"We welcome efforts by Beijing and Moscow to encourage Pyongyang to refrain from provocative rhetoric and threats," said White House spokesman Jay Carney.