The White House said Kofi Annan's resignation as mediator in Syria highlighted Syrian President Bashar al-Assad's refusal to abide by a UN-backed peace plan and the failure of Russia and China to hold Assad accountable at the UN Security Council.

"President Assad, despite his promise to abide by the Kofi Annan plan, continues to brutally murder his own people," Jay Carney, the White House spokesperson, told reporters aboard Air Force One on Thursday.

Carney also said the White House continues to believe that "Assad must go" and said it did not believe adding more weapons to the Syrian conflict would lead to a peaceful transition.

 
Syrians attending the mass burial of victims in the Syrian capital Damascus on August 1, 2012 [AFP]