Fresh allegations of potential war crimes by the Saudi-led coalition battling the Houthi rebels in Yemen are putting strain on flagging US support for the mission.

With the Pentagon already increasing public and private pressure on Riyadh to cut down on civilian casualties, the UN Human Rights Council released a report today that found “little evidence” that Saudi Arabia or the United Arab Emirates took basic steps to protect noncombatants. The UN says the three-year air war has killed at least 6,475 people, and probably many more.

In particular, the report castigated Saudi Arabia and the UAE for failing to consult no-strike lists that include refugee camps and hospitals. The two countries, along with the Yemeni government and its Houthi foes, are also accused of a spate of crimes including rape, forced disappearances and arbitrary detention.

The report, which urges the United States and Britain to stop providing weapons to the Saudi-led coalition, forced Defense Secretary Jim Mattis onto the back foot at the outset of a rare Pentagon press briefing today. Mattis said US support for aerial refueling and intelligence support to the Saudi-led coalition “is not unconditional.”