Sadiq Khan and Anas Sarwar have added to the pressure on Keir Starmer to back calls for a ceasefire between Israel and Hamas.
In separate statements on Friday, the Labour London mayor and Scottish Labour leader both called for a ceasefire.
Khan 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.”
Sarwar said: “There have been too many innocent lives lost in Israel and Palestine. We need a ceasefire now.”
Their interventions came amid a growing backlash among Labour MPs to Starmer’s response to the crisis in the Middle East.
The Labour leader angered many when, during an interview on LBC, he appeared to give his support to Israel cutting off water, fuel and food supplies to Gaza.
Many voters around the country were outraged and have made their views known to their local Labour MPs.
Starmer has since insisted he was supporting Israel’s right to defend itself in general terms rather than those particular tactics.
In the past week, however, the row has gained further momentum as demands grow for Labour to support a ceasefire in the war.
Starmer met with around a dozen Muslim Labour MPs and peers yesterday to hear their concerns.
In a statement afterwards, he would only say he backs US Secretary of State Antony Blinken’s call for “humanitarian pauses” in the fighting, rather than a full ceasefire, to let aid to Gaza get through.
Up to 100 Labour MPs - including 40 frontbenchers - have made their unhappiness known to Starmer’s office.
Khan said: “The terrible situation in Gaza now looks set to deteriorate even further. Thousands of innocent civilians - men, women and children have already been killed.
“And it’s becoming impossible for aid to reach the people who desperately need it. Substantial military escalation is now likely, which will only deepen the humanitarian disaster.
“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.
“Israel has a right to defend itself, to target those responsible for the appalling terror attack of 7 October, and to take action to free the hostages.
“The international community must redouble its efforts to get the hostages released.”
HuffPost UK revealed yesterday that Labour MPs have been offered security advice as tensions mount over the ongoing war.