Foreign Office minister Baroness Warsi has resigned from the government, saying she can "no longer support" its policy on Gaza.
She wrote on her Twitter feed that she was leaving with "deep regret".
Lady Warsi, who was previously chairman of the Conservative Party, became the first female Muslim cabinet minister when David Cameron took office in 2010.
She grew up in Dewsbury, West Yorkshire, and worked as a solicitor before entering politics.
Lady Warsi was demoted from the cabinet to a middle-ranking Foreign Office post in 2012. She was made minister for faith and communities at the same time.
She wrote on Twitter on Tuesday: "With deep regret I have this morning written to the Prime Minister & tendered my resignation. I can no longer support government policy on Gaza."
One of five daughters of Pakistani immigrants, Lady Warsi studied at Leeds University, later working for the Crown Prosecution Service before setting up her own legal practice.
Israel launched Operation Protective Edge on 8 July with the stated aim of ending rocket attacks and destroying tunnels used by Palestinian militants.
Gaza officials say the four-week conflict has killed 1,800 Palestinians. Some 67 Israelis have also died.
Lady Warsi has called on Twitter for more international action to end the crisis.
On 21 July, she wrote: "The killing of innocent civilians must stop. Need immediate ceasefire in Gaza. Leadership required on both sides to stop this suffering."
Three days later she added: "Can people stop trying to justify the killing of children. Whatever our politics there can never be justification, surely only regret Gaza."
Backbench Conservative MPs have been calling on David Cameron to take a more robust line with Israel amid concerns its actions are disproportionate.