At least three cables criticizing the administration's policy have been filed with the Department's internal "dissent channel", which was established during the Vietnam War and allows diplomats to raise concerns about policy anonymously with the Secretary of State, sources familiar with the matter said.

The criticism focuses on President Joe Biden's unwavering support for Israel in the aftermath of the Oct. 7 attacks by Hamas militants that killed 1,200 people, mostly civilians, the deadliest assault in the country's history.

In response, Israel has launched a relentless military campaign on Gaza, killing more than 11,000 Palestinians, according to Gaza's health ministry, unleashing the bloodiest chapter in years in the decades-old Israeli-Palestinian conflict.

Washington has rebuffed calls from Arab and Palestinian leaders and others to call on Israel to halt its assault on the Hamas-controlled Gaza strip, but it has urged for humanitarian pauses to allow more aid in and to evacuate Americans and foreigners.

In an emailed letter to the State Department employees, Blinken, having just returned from a nine-day trip to the Middle East and Asia, acknowledged the emotional toll the conflict has taken on the workforce but also the possible divisions within the ranks over policy.

"I know that for many of you, the suffering caused by this crisis is taking a profound personal toll," Blinken said in the letter obtained by Reuters.

"The anguish that comes with seeing the daily images of babies, children, elderly people, women, and other civilians suffering in this crisis is wrenching. I feel it myself," he said.

"I also know that some people in the Department may disagree with approaches we are taking or have views on what we can do better. We’ve organized forums in Washington to hear from you, and urged managers and teams to have candid discussions at posts around the world precisely so we can hear your feedback and ideas. I’ve asked our senior leadership to keep doing that."

"We’re listening: what you share is informing our policy and our messages."

HuffPost was the first to report on the email.

Blinken's letter comes amid protests in the United States and other countries calling for a ceasefire, and widespread concern among officials over the U.S. response to the Middle East crisis, which has included the public resignation of one State Department official who said he opposed continued lethal assistance to Israel.

More than 500 people who worked on Biden's 2020 election campaign last week published a letter, seen by Reuters, calling for the president to support an immediate ceasefire, and a group of congressional staffers held a vigil on Wednesday at the Capitol demanding a ceasefire, images on social media showed.

While some sources say there has been "deep frustration" among members of working level staff at the State Department, several U.S. officials say, while the Department leadership welcomes a diverse set of voices, it is unlikely to profoundly change Biden's policy.

In a briefing earlier on Monday, Department spokesperson Matthew Miller said Blinken has met with a number of people from different bureaus within the agency to hear what they think about the policy over Israel-Hamas war.

"He encourages people to provide feedback. He encourages people to speak up if they disagree. It doesn’t mean that we’re going to change our policy based on their disagreements," Miller said.