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.

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