The UK should stop selling arms to Saudi Arabia while Saudi actions in neighbouring Yemen are investigated, a draft report by MPs has said.
The Committees on Arms Export Controls said it was highly likely that weapons had been used to violate international humanitarian and human rights laws.
The draft report has been seen by the BBC's Newsnight programme.
The UK government said it had received assurances from Saudi Arabia but the committee said this was not sufficient.
Establish the facts
The government has faced sustained pressure to suspend the sale of weapons to the country amid claims that international humanitarian law has been breached in fighting between the Yemeni government, backed by Saudi Arabia, and Shia Yemeni rebels.
On Monday, Foreign Secretary Boris Johnson defended the selling of arms to Saudi Arabia for potential use in Yemen, insisting the export of weapons to the country would continue.
The Committees on Arms Export Controls is made up of four parliamentary committees - business, innovation and skills; defence; foreign affairs; and international development.
Its draft report, seen by Newsnight's Gabriel Gatehouse, said: "The weight of evidence of violations of international humanitarian law by the Saudi-led coalition is now so great, that it is very difficult to continue to support Saudi Arabia."
The committee said it seemed "inevitable" that such violations had involved arms supplied by the UK which would mean it was in violation of its own legal obligations.
'Within the boundaries'
The UK government said it operated one of the strictest arms licensing regimes in the world, and maintained it had received assurances from Saudi Arabia that it operated within the boundaries of international law.
The draft report concluded that those assurances were not sufficient and the UK should suspend exports until an international and independent inquiry could establish the facts.
Save the Children said it was calling on Foreign Secretary Boris Johnson to back a resolution to establish an international investigation when the UN Human Rights Council meets in Geneva later this month.
"This is a concrete opportunity finally to get to the bottom of alleged violations by all parties to the conflict, including the Saudi-led coalition, which investigations carried out by Saudi Arabia itself cannot deliver," spokeswoman Kirsty McNeill said.
"Children must always be protected in war, and now the UK government has a unique opportunity to remind the world that war can and must have limits."
Last month, aid agency Oxfam accused the British government of "denial and disarray" over an agreement to sell arms to Saudi Arabia, which could be used in Yemen.