Palestinian militants have a command center at Al-Shifa hospital in Gaza, the White House said Tuesday, backing up a key Israeli justification for military moves on the facility.
Hamas quickly slammed the comments, saying that Washington's statement was enabling Israel "to commit further brutal massacres targeting hospitals" in Gaza.
Hamas and Islamic Jihad operate a "command and control node from Al-Shifa in Gaza City," National Security Council spokesman John Kirby told reporters, citing US intelligence sources.
"We have information that Hamas and the Palestinian Islamic Jihad use some hospitals in the Gaza Strip, including Al-Shifa and tunnels underneath them to conceal and to support their military operations and to hold hostages," he said.
"We have information that confirms that Hamas is using that particular hospital for a command and control node and probably storage of equipment, weapons... That is a war crime."
Hamas blamed Washington for helping to fuel the conflict.
"These statements give a green light to the Israeli occupation to commit further brutal massacres targeting hospitals, with the goal of destroying Gaza's healthcare system and displacing Palestinians," the militant group said in a statement issued in English.
It added: "The United States bears direct responsibility for enabling Israel's genocidal war on Gaza."
The White House statement, echoed by the State Department and the Pentagon, comes as pressure ramps up on Israel over its blockade of the sprawling Al-Shifa compound, where doctors say patients and people seeking shelter are stranded in horrific conditions.
The United Nations estimates at least 2,300 people -- patients, staff and displaced civilians -- are inside and may be unable to escape because of fierce fighting near the facility.
Israel says it is not targeting the hospital itself, but has vowed to destroy Hamas in response to the attacks of October 7, which killed an estimated 1,200 people, mostly civilians, and saw 240 hostages being taken to Gaza.
The health ministry in Hamas-run Gaza says Israel's relentless assault has killed 11,320 people, also mostly civilians, including thousands of children.
Israel has long insisted that Hamas uses hospitals and other civilian facilities as cover, accusing the Islamist group of cynically using civilians as human shields.
But there is a growing global clamour for proof of the assertions, with horrifying stories of human suffering emerging daily from Al-Shifa.
The hospital's director said Tuesday scores of dead including children have been buried in a mass grave there.
Israel has so far declined to provide contemporaneous proof of its claims, so the US intervention Tuesday will bolster its position.
State Department spokesman Matthew Miller said Hamas had been "burying their command centers under hospitals for years," and called for the group to allow civilians to be evacuated.
"We would support an independent third party, a respected third party, to conduct those evacuations," he said.
"We know the government of Israel would support such a step as well. The question is, will Hamas allow patients to be evacuated from hospitals, or will they continue to be used as human shields?"
Al-Shifa's fate has become a major focus of the war.
Israel insists it must protect citizens after the worst attack in the country's 75-year history.
But Israel's critics point to the toll of a blockade and the near-relentless bombing campaign on long-suffering civilians in Gaza.