WASHINGTON - US President Barack Obama rejected Russian President Vladimir Putin's claim that Syrian rebels were responsible for an Aug. 21 chemical gas attack but, in an interview broadcast on Sunday, he welcomed Putin's diplomatic role in the crisis.

Obama, in an interview on ABC's "This Week With George Stephanopolous," defended his handling of the Syria crisis and dismissed criticism of his zig-zag approach to the issue as an argument about style.

Obama also said he and new Iranian President Hassan Rouhani had exchanged letters about the situation in Syria and that the Iranians understand the US concern about a potential nuclear-armed Iran "is a far larger issue" for the United States.

Obama and Putin have become unlikely allies on Syria after US threats to launch a military strike against Syria over the chemical weapons attack prompted a diplomatic initiative that has led to a framework deal on Saturday aimed at gaining control of Syria's poison gas stockpiles.

Obama said he welcomed Putin's involvement as helpful and said any deal on Syria must include a verifiable way to ensure that it gives up all its chemical weapons capacity.

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