The Israeli military said on Tuesday that it was highly likely that a slain American-Turkish activist was “unintentionally” struck by Israeli fire last week at a protest in the Israeli-occupied West Bank and expressed regret over her killing.

In a statement describing its initial inquiry into the matter, the military said that it had meant to target a person it described as a “key instigator” of the protest, which it called “a violent riot.”

Palestinians have long said that Israel uses excessive force against them at clashes and protests in the West Bank, but the death of the activist, Aysenur Eygi, has shined a spotlight on the issue.

The criminal investigation division of the military police has been investigating the episode and will share its findings with military prosecutors later, the Israeli military said. Ms. Eygi’s family has demanded that President Biden and other senior U.S. officials order an independent investigation to “ensure full accountability for the guilty parties,” saying that an Israeli inquiry was not adequate.

In his most forceful comments so far on Ms. Eygi’s killing, Secretary of State Antony J. Blinken said Tuesday that “no one should be shot and killed for attending a protest.”

“Israeli security forces need to make some fundamental changes to the way they operate in the West Bank, including changes to their rules of engagement,” he said at a news conference in London.

Ms. Eygi, who immigrated to the United States from Turkey as an infant and lived in Seattle, had recently arrived in the West Bank to join activists affiliated with the International Solidarity Movement, who demonstrate alongside Palestinians in the West Bank. On Friday, she joined the protest, in the northern West Bank village of Beita, where residents have been demonstrating for years — sometimes violently — against a settler outpost on lands claimed by the village. The Israeli government had recently said it would legalize the outpost.

The Israeli military said on Friday that soldiers had “responded with fire toward a main instigator of violent activity” who had thrown stones at Israeli forces and posed a threat to them. Witnesses at the scene did not deny that some protesters had hurled rocks at Israeli troops. But they said the clashes had finished by the time Ms. Eygi was shot, and that they had occurred in a separate location around 200 yards away.

Edward Wong contributed reporting from London.