Saudi arms 'investigation' needed, says Philip Hammond
Foreign Secretary Philip Hammond has called for "proper investigations" into Saudi airstrikes in Yemen.
He said UK weapons are being used and Saudi assurances of compliance with humanitarian law are "not enough".
UK sales to the Kingdom would halt if they are found to have breached international law.
His comments have been welcomed by the charity Oxfam, which has urged the UK to halt arms exports while allegations of war crimes are investigated.
Speaking to BBC Newsnight during a visit to Washington DC on Tuesday, Mr Hammond said he had raised the issue of air strikes with the Saudis in recent weeks.
Saudi Arabia denies targeting civilians during its bombing campaign in Yemen, which began in March.
"Obviously that denial alone is not enough," Mr Hammond said. "We need to see proper investigations.
"We need to work with the Saudis to establish that international humanitarian law has been complied with - and we have an export licensing system that responds if we find that it has not. We will then find that we cannot license additional shipments of weapons."
Civilians on 'firing line'
Josephine Hutton, Middle East programme manager at Oxfam, welcomed what she called a "change of heart from the government".
She said: "The humanitarian crisis in Yemen is worsening by the day. Civilians are in the firing line, not only by weapons but also by the ever-tightening blockade which is strangling the country's essential services and its economy. Britain needs to put all its diplomatic weight behind the push for peace."
The war in Yemen escalated in March, when a coalition led by Saudi Arabia entered the conflict on the side of the internationally recognised government to try to oust Houthi rebels from the capital Sana'a and other areas. All sides have been accused of targeting civilians.
Oxfam, Amnesty International and other organisations have called on the UK and the US to suspend the sale of weapons to Saudi Arabia while "damning evidence of war crimes" is investigated.
In September, BBC Newsnight reported from the aftermath of an airstrike on a water bottling plant in Yemen in which 13 civilians were killed. A spokesman for the Saudi-led coalition claimed the plant was a secret weapons factory.
Saudi Arabia is Britain's biggest market for defence exports, worth $1.7bn (£1.1bn) last year, according to IHS's Global Defence Trade Report.
Mr Hammond said the UK operated "one of the strictest export licensing regimes in the world".
"We only export weapons systems where all the criteria of our export licensing system are met," he told Newsnight.
David Cameron's government has championed the UN Arms Trade Treaty, which came into force in December and which prohibits states from exporting weapons that would be used for war crimes.
In a letter to the Daily Telegraph last month, Saudi Arabia's ambassador to the UK noted an "alarming change" in Britain's attitude towards his country, which he warned could lead to "serious consequences".
Special reports from BBC Newsnight on the crisis in Yemen: