The US ambassador to Israel has called Cabinet minister Bridget Phillipson "delusional" for claiming the UK played a "key role" in securing the ceasefire in Gaza.
The Education Secretary had insisted earlier on Sunday that the country was influential to peace efforts, saying important work had been carried out "behind the scenes".
Mike Huckabee, who was part of US President Donald Trump's negotiating team for the peace deal, mocked Ms Phillipson's assertion in a post on social media.
“I assure you she’s delusional. She can thank Donald Trump any time just to set the record straight,” he said in a post on X.
The public row between key figures in the UK and US Governments could prove awkward for Sir Keir Starmer as he prepares to join world leaders at a summit on Gaza co-chaired by Mr Trump on Monday.
Israel's deputy foreign minister Sharren Haskel also rejected Ms Phillipson's claim, hitting out instead at Britain's recognition of Palestinian statehood, which she said risked emboldening Hamas.
Speaking to broadcasters earlier on Sunday, Ms Phillipson, who is also running for the Labour deputy leadership, had said the UK "played a key role behind the scenes in shaping this".
Asked what this contribution involved, she told Sky News' Sunday Morning With Trevor Phillips: "These are complex matters of diplomacy that we are involved in.
"But we do welcome and recognise the critical role that the American government played in getting us to this point."
On Sunday afternoon, Ms Haskel criticised the decision to recognise Palestinian statehood and accused Britain of diminishing the prospect of peace by emboldening Hamas.
"The Government of the UK, Macron's plan, the whole conversation about declaring a Palestinian state - we disagree with you," she said.
Asked about Ms Phillipson's characterisation of the UK's efforts, the minister said: "Well, I have to contradict her words, unfortunately.
"Unfortunately, with the declaration of the Palestinian state during a very sensitive time two months ago when the teams were already around the table negotiating, when we truly believe we are able to reach a deal, the message that the UK Government sent Hamas was the message that the longer they continue this war, they will be rewarded."
The UK joined countries including France, Australia and Canada last month in confirming recognition of Palestinian statehood in a historic if largely symbolic move leaders said was intended to safeguard the prospect of a two-state solution.
The Prime Minister will attend the "signing ceremony" for the Gaza peace plan in Sharm El Sheikh in Egypt on Monday, where he is expected to heap praise on Mr Trump and the diplomatic efforts of Egypt, Qatar and Turkey.
Sir Keir will pay "particular tribute" to the US leader and partners in the region for "bringing us to this point" before calling for "swift progress towards phase two", Downing Street said.
French President Emmanuel Macron will also attend, the Elysee Palace confirmed on Saturday.
Meanwhile, former prime minister Sir Tony Blair, who was poised to potentially join a "Board of Peace" supervising governance of Gaza under the plans, met the deputy chief of the Palestinian Authority on Sunday.
Hussein Al-Sheikh said he had "confirmed our readiness to work with President Trump, Mr Blair" and other partners to secure the entry of aid and the release of hostages and prisoners, before starting on "recovery and reconstruction".
"We stressed the importance of stopping the undermining of the Palestinian Authority, and especially the return of the withheld Palestinian revenues and preventing the undermining of the two-state solution in preparation for a comprehensive and lasting peace in accordance with international legitimacy", he said in a post on X.
The 20-point plan brokered by the US president calls for Israel to maintain an open-ended military presence inside Gaza, along its border with Israel.
An international force comprising largely troops from Arab and Muslim countries would be responsible for security inside the enclave.
The Israeli military has said it will continue to operate defensively from the roughly 50% of Gaza it still controls after pulling back to agreed-upon lines.
Under the terms of the agreement, the first phase of the plan is expected to see remaining hostages returned to their families and Palestinian prisoners released from Monday morning.
The Government has already said there are no plans to send British troops to be part of the multinational force that will monitor the truce.
Asked whether Sir Tony had consulted Sir Keir about his possible role, Ms Phillipson said: "I'm afraid I simply can't answer that question."
Shadow foreign secretary Dame Priti Patel on Sunday dismissed the Prime Minister's visit to Egypt as a "photo opportunity".
"I think we have to be honest (about) the fact that Britain has had no role, no role whatsoever, under Keir Starmer's government, in even getting to this very seismic and momentous moment," she told the BBC.
"I think it's extraordinary that Keir Starmer apparently is going to Egypt tomorrow when we've got plenty of domestic issues that he should be resolving."
About 200 US troops have arrived in Israel, where they are expected to set up a centre to facilitate the flow of humanitarian aid and provide security assistance, the Associated Press reported on Saturday.
The Gaza war was triggered when Hamas-led militants launched a surprise attack on Israel on October 7 2023, killing some 1,200 people and taking 251 hostage.
In Israel's ensuing offensive, more than 67,000 Palestinians have been killed in Gaza and nearly 170,000 wounded, according to Gaza's Hamas-run Health Ministry, which does not differentiate between civilians and combatants but says around half the deaths were women and children.
The United Nations and many independent experts consider the ministry's figures to be the most reliable estimate of wartime casualties.