The senior Foreign Office minister Baroness Warsi has resigned over the Government's policy on the Gaza conflict.
Announcing her resignation this morning, the former Chair of the Conservative Party said that she had written to David Cameron "and tendered [her] resignation".
"I can no longer support Government policy on Gaza," she wrote.
Baroness Warsi, who in 2012 was also appointed by David Cameron as Minister for Faith and Communities, has regularly expressed her views on fighting between Israel and the Palestinians in Gaza on her Twitter feed, which is followed by more than 35,000 people.
On the 24 July, more than two weeks into the current conflict that has seen more than 1,800 Palestinians killed, she wrote: "Can people stop trying to justify the killing of children. Whatever our politics there can never be justification, surely only regret #Gaza."
Her resignation comes as yesterday Mr Cameron refused to condemn Israel's recent apparent air strike on a UN-run school in Rafah, Gaza as "criminal".
The attack, which killed at least 10 Palestinians including children, provoked recriminations from around the world, including the UN and Israel's long-time allies, the US.
Mr Cameron said it was "right" to condemn the air strike, but stopped short of endorsing UN Secretary-General Ban Ki-Moon's description of the attack as a "moral outrage and a criminal act".
Responding to Baroness Warsi's resignation today, fellow Conservative peer Lord Deben described her as a "class act in the House of Lords upon whom [the] Government relies".
"[The] Government will miss her command of the subject and of the House. She is a significant loss on a real matter of principle," he said.
Labour was also quick to respond to the news. Sadiq Khan, the shadow Justice Secretary, said it was "very courageous of my brave friend Sayeeda Warsi to resign over this Government's inexplicable silence and total weakness on the Gaza crisis".
His comments followed Ed Miliband's criticism of the Prime Minister over the weekend for failing to send a "clearer message to Israel" over the conflict.
On Saturday the Labour leader said it was "wrong" of Mr Cameron not to publicly oppose Israel's incursion into Gaza, adding: "His silence on the killing of hundreds of innocent Palestinian civilians caused by Israel's military action will be inexplicable to people across Britain and internationally."