Ending days of speculation over a possible second House of Commons vote on the issue, Cameron told British MPs the UK won't be part of any military strikes against Bashar al-Assad's regime.
"I accept that Britain can't be part, and won't be part, of any military action on that front but we must not in any degree give up our utter revulsion at the chemical weapons attacks that we have seen and we must press this point in every forum that we are a member," he said during Prime Minister's Questions in Parliament here.
He, however, warned that the world was letting the Syrian people down and he regretted last week's vote on military action, which the government lost.
"My only regret of last week is that I don't think it was necessary to divide the House on a vote that would have led to a vote but he [Opposition leader Ed Miliband) took the decision that it was," he said.
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The Labour leader said there was public support "for Britain taking every diplomatic, humanitarian effort to help the Syrian people".
In response, Cameron said President Assad would not consider peace talks unless he came under sustained pressure at home and abroad.
Meanwhile, the UK Ministry of Defence has denied media reports that France has sent two spy planes to the RAF Akrotiri base in Cyprus, which is less than 200 miles from Syria.