'Please! This isn't complicated!' says Kerry on Assad's chemical weapons claims

Secretary of State John Kerry has ridiculed Syrian President Bashar al-Assad for claims that his regime did not use chemical weapons last month.

Assad in an interview with Fox news had claimed that the rebels might have been behind 21st August attack, as he urged the United Nations to get tough when it convenes next week.

Kerry had a pithy response to Assad's claims and the Russian government that the opposition used sarin gas: 'Please'.

'Sarin was used and it killed people,' Kerry said, adding that the world can decide whether it was used by the regime, which has used chemical weapons before, the regime which had the rockets and the weapons.

Kerry made a surprise appearance at the daily State Department briefing on Thursday ahead of the U.N. meeting next week in New York.

U.S. diplomats will work on a U.N. resolution to enforce a new agreement that would have the Assad regime submit its chemical weapons to international control.

But Kerry was evidently frustrated by claims by the Syrian and Russian governments that Assad's regime was not behind the deadly attack on Aug. 21. which prompted the stand-off with the U.S.

In the interview, Assad admitted he has chemical weapons but denied that his government was behind the attack, continuing to push the theory that the opposition was behind the strike.