Labour London Mayor Sadiq Khan has called for a ceasefire in the Israel-Hamas war, putting him at odds with his party leader Sir Keir Starmer.
Sir Keir has stopped short of making such a call, instead backing "humanitarian pauses" in the conflict as a way to help aid reach Gaza.
Scottish Labour leader Anas Sarwar has also backed a ceasefire, adding pressure on him to change stance.
However, Labour frontbencher Steve Reed has defended Sir Keir's position.
The shadow minister said humanitarian pauses would allow aid to enter Gaza "without stopping Israel taking action to disable the terrorists who attacked them in the first place".
"A ceasefire would stop Israel from doing that, and would leave the terrorist capability intact," he added.
In a statement earlier, Mr Khan said Israel had a "right to defend itself" following the "appalling terror attack" of 7 October.
Israel began its bombing campaign in Gaza, cut off electricity and most water, and stopped imports of food, fuel and other goods in retaliation for a cross-border attack by Hamas on 7 October, in which at least 1,400 people were killed and 224 taken hostage.
Gaza's Hamas-run health ministry says 7,000 people have been killed in the territory since then and that its health system is facing total collapse, with a third of hospitals not functioning and the rest only treating emergency cases.
Mr Khan said a ceasefire would "allow the international community more time to prevent a protracted conflict in the region and further devastating loss of life".
In a video, Scottish Labour leader Mr Sarwar said: "We are all so desperate for peace and are desperate to see the end of violence."
"We need to see the immediate release of hostages, immediate access to humanitarian supplies... and the immediate cessation of violence with an end of rocket fire into and out of Gaza," he added.
"And let me be clear, that means a ceasefire right now," he added.
By calling for humanitarian pauses, Sir Keir is in line with Prime Minister Rishi Sunak, the US and the EU.
Asked why the UK was not calling for a cessation of violence, Education Secretary Gillian Keegan told ITV that the government would not "cross that line of telling Israel it has anything but the right to defend itself".
She said a humanitarian pause would enable British citizens to leave Gaza.
Mr Sunak told reporters on Thursday that the Foreign Office is in contact with around 200 UK nationals in Gaza.
The Labour leader's overall stance on the Israel-Gaza conflict has also led to growing discomfort in his party.
He triggered anger earlier this month, when in reply to an interview question on whether it was "appropriate" for Israel to cut off the supply of power and water to Gaza, he said: "I think that Israel does have that right."
"Obviously everything should be done within international law, but I don't want to step away from the core principles that Israel has a right to defend herself," he added.
A spokesman for the Labour leader later said he had only meant to say Israel had a general right to self-defence.
At least 19 councillors have since quit Labour in protest. In Oxford, resignations have led to Labour losing its majority on the local council.
In Westminster, 39 Labour MPs - including shadow minister Imran Hussain - have signed a parliamentary petition calling for an "immediate de-escalation and cessation of hostilities".
Earlier this week, Sir Keir met with Muslim MPs in a bid to reduce tensions over the issue.
Senior figures adding their voice to calls for a ceasefire is certainly uncomfortable for the Labour leadership.
Especially following a recent conference where their outward message was one of unity - a shift away from past divisions and factions within senior ranks of the party.
So far, most of the dissent in the party has been from councillors while dozens of Labour MPs have now said publicly they want a ceasefire.
While there's been chatter of frontbenchers considering resignations, that hasn't transpired so far.
Certainly, senior figures in the party have told me that engagement with concerned MPs is ongoing and that the party is trying to support those who have received threats or abuse as a result of the party's position.
They don't deny that lots of people are very concerned. But they argue that at the same time the last thing many in the party want to see is an internal fight - especially if there is an awareness that resignations may not change the leadership's position
Nor can the Labour leadership's position really change what is going on in Israel and Gaza.
But for some it feels more like a matter of principle than actually changing anything.
Some may begin to feel the heat more from constituents as MPs go off on another recess break.
