More than 1,000 officials in the US Agency for International Development (USAID) have signed an open letter urging the Biden administration to call for an immediate ceasefire in the conflict between Israel and Hamas, according to a copy of the letter seen by Reuters.

The letter is the latest sign of unease within the US government over President Joe Biden’s unwavering support for Israel.

Washington has rebuffed calls from Arab and Palestinian leaders and others to call for Israel to halt its assault on the Gaza Strip which has killed more than 11,000 Palestinians, including over 4,500 children, according to Gaza’s health ministry.

“As development, public health, and humanitarian assistance professionals, we are alarmed and disheartened at the numerous violations of international law; laws which aim to protect civilians, medical and media personnel, as well as schools, hospitals, and places of worship,” the letter reads.

The letter, published on Nov 2, had now garnered 1,029 signatures from staff of the US aid agency. Signatories names are hidden but the letter shows it was signed by officials in many of the agency’s bureaus in Washington as well as officials posted around the world.

USAID did not immediately respond to a request for comment.