The Tory party has reacted to the "unnecessary" resignation of Baroness Warsi over concerns about the government's policy in Gaza.

The former senior foreign office minister said she has left the party "with deep regret" adding "I must be able to live with myself" for decisions taken and supported while in government.

"By staying in Government at this time I do not feel I can be sure of that," she wrote in her resignation letter to David Cameron.

Warsi, who was previously Chairman of the Conservative Party, was one of the most senior female members of the Cabinet and became the first female Muslim minister when Cameron and the coalition government were voted into power in 2010.

She described the government's current stance on the Gaza conflict as "morally indefensible". She wrote in her resignation letter that Britain's response to the Gaza crisis could form a "basis for radicalisation [which] could have consequences for us for years to come".

Warsi has been vocal about Cameron's apparent failure to condemn Israel's actions during the ongoing conflict.

She recently tweeted: "Can people stop trying to justify the killing of children. Whatever our politics there can never be justification, surely only regret."

Cameron, who is on holiday, has yet to personally respond to Warsi's resignation. However, Downing Street said the prime minster "regrets" her decision to stand down and is "grateful for the excellent work that she has done both as a minister and in opposition".

A spokesperson added: "Our policy has always been consistently clear - the situation in Gaza is intolerable and we've urged both sides to agree to an immediate and unconditional ceasefire."

Elsewhere, chancellor George Osborne is reported to have described Warsi's decision to resign as "disappointing and frankly unnecessary".

He added: "The British government is working with others in the world to bring peace to Gaza and we do now have a tentative ceasefire which we all hope will hold."

London mayor Boris Johnson, a fellow Conservative, said he has a "great respect" for Warsi and hopes she returns to government soon.

When asked about Israel's actions in Gaza, Johnson told LBC Radio he believes their actions are "disproportionate...ugly [and] tragic".

"In having that opinion, I'm merely echoing what everyone else is saying at the moment," he added.

"It is obviously horrifying and I want it to stop and pray it stops."

Deputy prime minister Nick Clegg said it was no "secret" that there are difference of opinions surrounding Gaza inside government.

He added: "Sayeeda Warsi clearly feels very strongly about this and has explained it to the prime minister in her own words. I believe it is right for Britain to be unambiguous in our condemnation of Hamas's indiscriminate firing of rockets but also very forceful and outspoken about Israel. The bombing of three UN schools is a complete outrage."

When asked whether he agreed with Warsi's view that Cameron has not been critical enough of Israel, Clegg added: "Clearly the prime minister and I take different views on this and we always have done."