"We're encouraging both sides to participate in that investigation so that we can get down to why this happened," US ambassador Linda Thomas-Greenfield said.

Washington's "highest priority is the protection of American citizens and the protection of journalists," she added.

The Qatar-based Al Jazeera TV channel charged that Israeli forces deliberately and "in cold blood" shot veteran reporter Abu Akleh, 51, in the head during the unrest in the Jenin refugee camp.

But Israel's Prime Minister Naftali Bennett suggested that "armed Palestinians" were "likely" responsible.

Thomas-Greenfield said she had been interviewed by Abu Akleh during a visit to the region last year and had "extraordinary respect for her."

State Department spokesman Ned Price added on Twitter "we are heartbroken" by Abu Akleh's death.

"Those responsible must be held accountable. Her death is an affront to media freedom everywhere," he said.