Foreign Office minister Baroness Warsi has dramatically quit the government, saying that she "can no longer support Govt policy on Gaza".
Writing on Twitter, she said: "With deep regret I have this morning written to the Prime Minister & tendered my resignation. I can no longer support Govt policy on Gaza."
In her letter to the Prime Minister, Warsi wrote: "Our policy in relation to the Middle East Peace Process generally but more recently our approach and language during the current crisis in Gaza is morally indefensible, is not in Britain's national interest and will have a long term detrimental impact on our reputation internationally and domestically."
"I believe our approach in relation to the current conflict is neither consistent with our values, specifically our commitment to the rule of law and our long history of support for international justice."
Insisting her decision to resign "has not been easy", Warsi said that Cameron would continue to have her "personal support as leader of the Conservatives to ensure that our party evolves to meet the challenges we face in Britain today".
Warsi became the first Muslim to sit in the Cabinet when she was made Conservative Party co-chairman by David Cameron following the 2010 general election.
She was subsequently moved to the post of Minister of State at the Foreign Office and Minister for Faith and Communities in Cameron's 2012 re-shuffle in a move widely regarded as a demotion.
Warsi is the first minister to quit "on principle" since the coalition was formed in 2010, with her resignation coming in the wake of attacks on the prime minister's handling of the Gaza crisis by Labour leader Ed Miliband - and a 72-hour humanitarian truce agreed between Israel and Hamas in Cairo on Monday evening.
Last week, however, Channel 4 News reported that FCO officials believed Warsi had "deep reservations and concerns about government policy" on Gaza.
In response to Warsi's resignation, deputy prime minister Nick Clegg said: "it's the first I have heard of it". The Lib Dem leader said that it was an "open secret" that there were "different opinions and emphases" among ministers "in reaction to bloodshed in Gaza".
London Mayor Boris Johnson said during his LBC radio phone-in this morning that her resignation was "very sad" and hoped she would return to government.
While Johnson - who described himself as a "passionate Zionist" said that politicians across the political spectrum were horrified at what had been happening in Gaza - he went on to condemn the Israeli action as "disproportionate" - a word Cameron and Foreign Secretary Philip Hammond have consistently avoided.
Tory MP Michael Fabricant said on Twitter that he was "sad" that Warsi had quit the government, adding: "I know she has v strong views on Muslim issues. But DC [David Cameron] is right on Gaza."
More to follow...