Liz Truss has given an "unequivocal commitment" to increase defence spending - hours after a minister threatened to resign if the Prime Minister U-turned.
The Prime Minister's comments came during a meeting of the European Research Group of MPs on Tuesday evening and amid weeks of turmoil in No10.
According to the ERG chairman, Mark Francois, Ms Truss told those present she was committed to spending 3% of national income on defence by 2030.
"We were delighted to hear her make an unequivocal commitment," he said. "She was very clear that that commitment remained."
Earlier James Heappey, a defence minister, said he would quit the government if Ms Truss U-turned on the pledge she made in her leadership campaign.
He added: "We need to be spending 3% of our GDP on defence of our nation by 2030 because there is no prosperity without security".
Defence secretary Ben Wallace - tipped as a potential successor to Ms Truss if she resigns - would also be under pressure to resign if the pledge was abandoned.
Despite the commitment on defence, the government is threatening to abandon the state pension triple lock - a move that would amount to yet another U-turn.
No10 refused four times today to guarantee it would stay in place as the new Chancellor Jeremy Hunt ordered government departments to find "efficiency" savings.
After the ERG meeting on Tuesday evening, the Prime Minister's deputy press secretary also said that Ms Truss told MPs it was "painful" to axe her tax-slashing programme - but did it "because she had to".
They added: "Touching on recent days, she talked about her disappointment in not being able to follow through on the tax cuts, although she stressed that of course, the NICs (National Insurance Contributions) cut has gone through."
"She said she found it painful and that she did it because she had to."
They also revealed Ms Truss had hired David Canzini - one of Boris Johnson's former aides - to help the No1o operation after weeks of chaos.
The deputy press secretary did not specify the role of Mr Canzini, an ally of the electoral strategist Sir Lynton Crosby, but said he would be "helping the Prime Minister" as part of her political team in No10.
It comes as some Tory MPs have called on the Prime Minister to resign after sacking her chancellor Kwasi Kwarteng on Friday and ripping up her economic agenda.
According to the Guardian, Michael Gove, a former cabinet minister who has clashed with Ms Truss, also suggested at an event on Tuesday her departure was inevitable.
When the host said they thought it was "no longer a question of whether Liz Truss goes, but when she goes", Mr Gove said she was "absolutely right".
He was also said to have joked that "we all know now" why Ms Truss had been given the nickname "the human hand grenade".
But on Tuesday evening the Business Secretary Jacob Rees-Mogg left the ERG meeting in Westminster, claiming it went "extremely well".
Mr Francois also said the meeting had been "positive", saying the Prime Minister was "open" and "answered every question that she was asked directly".
"She was absolutely committed to see a robust outcome regarding the Northern Ireland Protocol.
"Very, very clear about that. Remember that she, when she was foreign secretary, was involved in toughening up that legislation."
