WASHINGTON/MOSCOW- An escalating crisis in Syria, echoing with Cold War-style recriminations, has badly frayed US-Russian relations at a delicate time, just as US President Barack Obama and Russian President Vladimir Putin try to renew their relationship.

US charges that Russia is arming the Syrian government as it attacks its opponents with lethal force, and Moscow's blocking of tougher action against Damascus, appear to indicate that tough times are ahead for Putin's relationship with Obama and, perhaps, his successor.

The fiercely nationalist Putin, who re-assumed the Russian presidency last month, is due to meet Obama at a G20 summit in Mexico early next week, their first encounter in three years. There is growing skepticism the two men can find common ground on Syria or other festering disputes.

Obama has touted the "reset" of relations with Russia, which came during the term of Putin predecessor Dmitry Medvedev, as one of his signature foreign policy achievements.

But Washington finds itself increasingly at odds with Moscow on issues from Syria and Iran to missile defense and human rights. Putin shows no sign of backing away from the anti-Western rhetoric and positions that have long been his hallmark.

That could set the stage for an uncomfortable meeting in Los Cabos, Mexico.

"The point is to break the ice, score a few political points but not have any kind of diplomatic blow-up in the process," said Matthew Rodansky, a Washington-based Russia expert at the Carnegie Endowment for International Peace.

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