London mayor Sadiq Khan, Scottish Labour leader Anas Sarwar and Greater Manchester mayor Andy Burnham are among those who want the Labour leadership to strengthen its position and back a full cessation of violence between Israel and Hamas.
Sir Keir is united with Rishi Sunak, the US, and most recently the EU in pushing for “humanitarian pauses” in the fighting, while supporting Israel’s right to defend itself against the militants who launched a wave of bloodshed in the country earlier this month, killing more than 1,400 people, according to authorities.
Politics Live: Pressure mounts on Keir Starmer as trio of top Labour figures call for Gaza ceasefire
But the Labour leader has angered MPs for not going further, with dozens urging him to back a ceasefire to prevent the conflict from escalating.
On Friday Mr Khan, who became the first-ever Muslim mayor of London in 2016, said: “I join the international community in calling for a ceasefire. It would stop the killing and would allow vital aid supplies to reach those who need it in Gaza.
“It would also allow the international community more time to prevent a protracted conflict in the region and further devastating loss of life.”
Mr Khan said Israel did have the right to defend itself, but warned the “terrible situation in Gaza now looks set to deteriorate even further”.
“A widespread military escalation will only deepen the humanitarian disaster. It will increase human suffering on all sides. No nation, including Israel, has the right to break international law.”
Scottish Labour leader Mr Sarwar, who in 2021 became the UK’s first Muslim to lead a political party, made the same demand with his own video just a few hours later.
He said there must be an “immediate cessation of violence, with an end of rocket fire into and out of Gaza”, so that aid can be delivered and hostages released.
“Let me be clear, that means a ceasefire right now,” he said.
Shortly afterwards Mr Burnham, deputy mayor Kate Green and the 10 leaders of Greater Manchester released a joint statement also calling for a ceasefire “amid the humanitarian disaster unfolding in Gaza”.
The group said they “condemn unreservedly” the Hamas attacks on 7 October and that Israel “has the right to take targeted action within international law to defend itself”.
But they added: “We also have profound concerns about the loss of thousands of innocent lives in Gaza, the displacement of many more and widespread suffering through the ongoing blockade of essential goods and services.
“It is vital that urgent support and humanitarian aid is allowed into the area.”
Shadow environment secretary Steve Reed had earlier said he “empathises” with MPs angry about the party leadership’s stance on the crisis in Gaza, but stood by the position taken by Sir Keir.
The shadow frontbench member told Sky News that if the attack Israel suffered had happened in the UK: “Our state would have sought to defend ourselves to protect our citizens by dismantling the capability of a terrorist organisation that carried it out. That applies to Israel too, they have the right under international law to do that.”
Party sources also made clear Sir Keir was not about to strengthen his position.
Tensions have been growing not only over his resistance in calling for a ceasefire, but also over his previous remarks in which he appeared to suggest Israel had the right to cut off power and water in Gaza.
The comments, which he has since rowed back from, prompted resignations among Labour councillors and angered the party’s MPs, even those on the frontbenches as shadow ministers.
Sir Keir has been holding meetings within his party to soothe some of the anger, including in talks with Muslim Labour MPs in parliament on Wednesday. They urged him during the “firm” exchange to back a ceasefire, believing the British public support the move as well.