British Government analysis has indicated that British-made cluster bombs have been used by Saudi Arabia-led forces in the war in Yemen.
Britain's Defence Secretary Michael Fallon is among ministers to have been made aware of the analysis, sources told the Guardian.
The British Government said it takes the allegations "very seriously" and has raised them with the Saudi-led coalition.
The analysis comes after the prime minister of Yemen's rebel Houthi government accused the UK of "war crimes" for supplying arms.
Media reports have repeatedly suggested cluster bombs made in the UK had been used in the war.
Because of their extraordinary risk to civilians, cluster bombs were banned in 2010 in an international treaty signed by Britain.
The UK's signature on the Cluster Munitions Convention also means it must be committed to preventing the banned weapon's use by other nations.
Rebel PM Abdel-Aziz bin Habtour previously said the UK Government was profiting from the humanitarian crisis by selling munitions.
He told Sky News: "They have sold cluster bombs to Saudi Arabia.
"They know the Saudis are going to drop them on Yemen ... in Sa'adah and in Sana'a and other provinces.
"I don't think they are guilty of war crimes, I believe so. They are participating in the bombing of Yemen people."
The Ministry of Defence declined to comment on the latest claims but a government spokesman said: "The Government takes such allegations very seriously.
"We have analysed the case carefully using all available information, considering all possibilities, and raised the issue with the Saudi-led coalition."