A Foreign Office minister who was the first Muslim to sit in the British cabinet dramatically resigned on Tuesday over what she called the government's "morally indefensible" policy on Gaza.
The surprise decision by Baroness Sayeeda Warsi, who also had responsibility for faith and communities, heaped pressure on Prime Minister David Cameron to take a tougher line against Israel over its actions in Gaza.
The coalition government has faced sustained criticism in recent days, led by the main opposition Labour party, that it has not spoken out strongly enough over the conflict.
"Our approach... 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," Warsi wrote to Cameron in her resignation letter.
She said there was "great unease" in the Foreign Office, where Philip Hammond took over as foreign secretary from William Hague last month, about how recent policy decisions had been made.
"Nearly 400 innocent children killed, we still cannot find the words to say we condemn this," she later told Channel 4 news, adding that there was "unease" in the ranks of the Conservative Party and that another minister had talked of resigning.
In his letter responding to the resignation, Cameron expressed regret that Warsi had not informed him of her decision before announcing it on Twitter.
"I understand your strength of feeling on the current crisis in the Middle East -- the situation in Gaza is intolerable," the prime minister wrote.
He added: "Of course, we believe that Israel has the right to defend itself.
"But we have consistently made clear our grave concerns about the heavy toll of civilian casualties and have called on Israel to exercise restraint, and to find ways to bring this fighting to an end."
He thanked Warsi for her service, saying she should take pride in her achievements "and especially for being the first Muslim woman in any British cabinet".
Other ministers were less diplomatic and questioned the timing of the resignation, as a 72-hour truce took hold in Gaza following four weeks of fighting.
"I do find it rather surprising that she has chosen now, this particular moment, to take this step when, in fact, we are now at long last seeing some relief, seeing some progress on the issues about which she was so passionately concerned," said Hammond.
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Finance minister George Osborne, a close ally of Cameron, called her resignation "disappointing and frankly unnecessary".
- 'Inexplicable' silence on Gaza -
Support however was offered by Deputy Prime Minister Nick Clegg, leader of junior coalition partners the Liberal Democrats, who said he shared Warsi's concerns and called for licences to export arms to Israel to be suspended.
"The actions of the Israeli military... breach the conditions of those export licenses and that's why we want to see them suspended pending a wider review of whether they should be revoked more permanently in the long run," Clegg said.
The prime minister's office on Monday said it was reviewing the licences, but Clegg said an announcement should be made "very shortly".
Warsi's star has dimmed in recent years, but she was once a high-profile example of Cameron's desire to diversify his Conservative party away from its traditional white, male base.
Her parents were Pakistani immigrants and she trained as a lawyer before being made a member of parliament's upper House of Lords in 2007.
She was appointed to Cameron's cabinet -- the powerful inner circle of government ministers -- when his coalition government took power in 2010, but was moved out in 2012.
Warsi describes herself on her website as "best known for being the first Muslim to serve in a British cabinet and the foremost Muslim politician in the Western world".
Labour leader Ed Miliband last week accused Cameron of "inexplicable" silence over the suffering of Palestinian civilians in a conflict that has killed at least 1,867 Palestinians and 67 people in Israel.
Miliband said on Tuesday: "I think Baroness Warsi has acted with principle and integrity. People around Britain have been shocked by the suffering we have seen in Gaza.
"David Cameron is right to condemn Hamas as a terrorist organisation but he needs to break his silence on Israel's indefensible actions."
On Monday, Cameron said the United Nations was "right" to condemn an air strike near a school in Rafah on Sunday which killed 10 people but would not say whether he thought it was a "criminal" act.