Fifty-one U.S. diplomats have called for the Obama administration to increase direct attacks against the government of Syrian President Bashar Assad, according to an internal State Department memo obtained by the New York Times.

In it, the group of midlevel State Department officials say the U.S. should use “stand-off and air weapons, which would undergird and drive a more focused and hard-nosed U.S.-led diplomatic process.” (Stand-off weapons are missiles or bombs launched from a distance outside the range of defending forces' return fire.)

The memo comes from the State Department’s so-called dissent channel, which was established during the Vietnam War to let officials register disagreements with official policies without fear of reprisals. While dissent memos are common, the number of diplomats that have signed the Syria memo is “extremely large, if not unprecedented,” the New York Times wrote.

“It’s embarrassing for the administration to have so many rank-and-file members break on Syria,” a former State Department official who worked on Middle East policy, told the Wall Street Journal, which also reviewed the memo. 

The absence of high-ranking officials in the memo is unsurprising because they typically speak more freely among themselves. Secretary of State John Kerry has himself called for a stronger American response to the Syrian civil war, which has claimed 400,000 lives and displaced millions of people since it started in March 2011.

The Obama administration has been hesitant to dive more deeply into the Syrian conflict, with its complex mix of factions, including the Islamic State group and other extremists that have been wreaking murderous havoc across Syria and Iraq. Russia supports Assad, further complicating efforts to oust him.

“Many people working on Syria for the State Department have long urged a tougher policy with the Assad government as a means of facilitating arrival at a negotiated political deal to set up a new Syrian government,” Robert S. Ford, a former ambassador to Syria, told the Times.

Last week, Assad vowed to take back territory lost to his enemies and has continued to block humanitarian convoys despite a months-old ceasefire orchestrated by Western allies that never took hold.