WASHINGTON - Sharp policy clashes over fugitive leaker Edward Snowden and Syria may be exacerbated by apparent personal animosity when President Barack Obama and Vladimir Putin come face-to-face in Russia this week.
Obama will arrive in St Petersburg on Thursday for the G20 summit, after canceling a one-on-one encounter with Putin in Moscow, as a string of policy rows ranging from human rights to geopolitics rage between the Kremlin and the White House.
The testy personal relationship between Putin and Obama, and the diverging policy agendas, have put paid to the "reset" of relations which Obama engineered with former Russian president Dmitry Medvedev early in his first term.
The G20 summit of developed and developing nations comes with many analysts diagnosing the state of US-Russia relations as at their worst since the end of the Cold War.
While US officials were infuriated by Russia's offer of asylum to Snowden, who leaked National Security Agency snooping secrets, they said Obama cancelled the Moscow summit because of a lack of progress across a wide range of issues.
But it is largely Snowden, and Russia's support for its last major Middle Eastern ally Syria, that have brought the relationship to its current low.
Frigid personal ties between Obama and Putin were in evidence when the two held an awkward photo op when they met in Northern Ireland at the G8 summit in June.
Then a few weeks ago, Obama declared that he did not have a bad personal relationship with Putin, but then went on to mock his counterpart as "the bored kid at the back of the classroom."
The New York Times reported that Putin was infuriated by the comment. "The good news is that this is not the Cuban Missile Crisis," said Andrew Kuchins, a Russia expert at the Center for Strategic and International Studies.
"But one thing is clear to me - that this is the worst personal relationship between US and Russian, perhaps even US and Soviet, leaders in history," Kuchins said.
"I really think these two guys, Mr Putin and Mr Obama, don't like each other at all. I think there's a deep degree of disrespect."