Story highlights The boys' relatives blame the Israeli military for the killings

The Israeli military says it fired no live rounds during the protests

"The killings may amount to extrajudicial executions under human rights law," the U.N. says

It calls for a prompt, independent, impartial and transparent probe

Two Palestinian teens killed in the West Bank presented no direct threat when they were shot last week, the United Nations said Friday in a preliminary report.

Nadeem Nouwarah, 17, and Mohammad Odeh Salameh, 16, were killed during protests on May 15 on the anniversary of the "Nakba," a day commemorating the displacement of Palestinians that accompanied the creation of Israel after the 1948 Arab-Israeli war.

Six hours of raw video distributed by advocacy organization Defense for Children International and reviewed by CNN shows the boys were shot on the same patch of asphalt. Their deaths were 73 minutes apart.

The boys' relatives blame the Israeli military for the killings.

"The killings may amount to extrajudicial executions under human rights law as well as willful killings under international humanitarian law, the U.N. High Commissioner for Human Rights said in a statement on Friday.

It called for a prompt, independent, impartial and transparent investigation.

"Our office has repeatedly raised its concerns about the excessive use of force by Israeli security forces and the lack of accountability for such incident," the statement said. "We also urge Israel to make public the findings of this investigation and any steps regarding accountability that are taken."

But an Israeli military spokesman said its forces fired no live rounds during clashes where the boys were killed.

"During that demonstration that was extremely violent, the Israeli Defense Force used crowd-control methods and riot-dispersal means to prevent and control the overflow of the violence," Lt. Col. Peter Lerner said.

"The preliminary IDF inquiry indicates that no live fire was shot at all Thursday during the riots in Beitunya, and we have to determine what caused this result," Lerner added.

The State Department joined several human rights groups calling for an investigation.