The Government is "deeply concerned" about the possible use of UK munitions by the Saudi air force in strikes on civilian targets in Yemen's civil war, Boris Johnson has said.
The Foreign Secretary said he did not believe a "threshold has been crossed" requiring the suspension of British arms sales to Saudi Arabia.
However he said that the depth of concern in Whitehall about the mounting civilian death toll should not be underestimated.
Britain has been under pressure to halt military exports to the Saudis who are heading a regional coalition supporting the Yemeni government against Iranian-backed Houthi rebels amid reports they have repeatedly hit civilians.
A United Nations panel found earlier this year that there had been "widespread and systematic" attacks by the coalition on civilian targets in violation of international humanitarian law.
Appearing on BBC1's The Andrew Marr Show, Mr Johnson acknowledged there were "very difficult questions" which ministers had to address about the use of UK munitions and technology in the conflict.
"So far we do not believe there has been a clear risk of breach of international humanitarian law," he said.
"People should not underestimate the concern we have about this. We are deeply concerned. I had a conversation only last night with the Saudi foreign minister, my counterpart, about this.
"Of course we are making representations the whole time. At the moment we do not think the threshold has been crossed."
Mr Johnson confirmed British advisers were continuing to give "general advice" to the Saudis on targeting in an attempt to avoid more civilian casualties, but said they were not involved in target selection.
"We are not involved in the targeting. We are not actually in the room looking at targets. We are trying to help them avoid breaches of international humanitarian law by giving them guidance about how targeting should work," he said.