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:
We have to look at all the options. We discussed this in the National Security Council yesterday. We have made no decision to change our current policy, and we have an EU arms embargo.
We are very much committed to intensifying our efforts, sending humanitarian aid. We will discuss with the opposition today giving them more non-lethal assistance - not arms, but other practical assistance we can send that helps save lives.
But of course, we will discuss with our European partners the future of the arms embargo. We have made no decision to change that so far.