As Israel pounded northern Gaza with air strikes last October and ordered the evacuation of more than a million Palestinians from the area, a senior Pentagon official delivered a blunt warning to the White House.

The mass evacuation would be a humanitarian disaster and could violate international law, leading to war crime charges against Israel, Dana Stroul, then the deputy assistant secretary of defense for the Middle East, wrote in an Oct. 13 email to senior aides to President Joe Biden. Stroul was relaying an assessment by the International Committee of the Red Cross that had left her “chilled to the bone,” she wrote.

Reuters reviewed three sets of email exchanges between senior U.S. administration officials, dated Oct. 11 to 14, just days into the crisis. The fighting has led to more than 40,000 deaths in Gaza and spurred U.S. protests led by Arab-Americans and Muslim activists.

The emails, which haven’t been reported before, reveal alarm early on in the State Department and Pentagon that a rising death toll in Gaza could violate international law and jeopardize U.S. ties in the Arab world. The messages also show internal pressure in the Biden administration to shift its messaging from showing solidarity with Israel to including sympathy for Palestinians and the need to allow more humanitarian aid into Gaza.