The head of the Western-backed Syrian National Coalition Moaz al-Khatib has announced his resignation, saying in a statement he had taken the step so he could "work with freedom".
"I had promised the great Syrian people and promised God that I would resign if matters reached some red lines," the rebel leader said in a statement posted on his official Facebook page. He did not explain what had prompted his resignation.
"Now I am fulfilling my promise and announcing my resignation from the National Coalition in order to be able to work with freedom that cannot be available within the official institutions," he added.
William Hague has reiterated that Britain will not provide arms to the Syrian opposition, ahead of his meeting today with a group of rebel leaders in London, but said they will discuss the possibility of the UK providing more non-lethal assistance.
He told BBC Radio 4's Today programme:
William Hague will today meet Syrian rebel leaders fighting to topple president Bashar Assad's brutal regime.
The Foreign Secretary will urge the group to develop a clear plan for political transition in Syria when he opens the London talks.
He will also press for the need to respect human rights and "win over the middle ground of opinion" in the nation amid the spiralling violence meted out by the regime.