JERUSALEM (AP) – An American demonstrator was critically wounded Friday in a clash between protesters and Israeli troops over Israel’s West Bank separation barrier.

Peace activists with the International Solidarity Movement said Tristan Anderson, of the Oakland, Calif., area, was struck in the head with a tear gas canister fired by Israeli troops. The military and the Tel Aviv hospital where Anderson was taken had no details on how he was hurt. “He’s in critical condition, anesthetized and on a ventilator and undergoing imaging tests,” said Orly Levi, a spokeswoman at the Tel Hashomer hospital. She described Anderson’s condition as ‘life-threatening.”

The protest took place in the West Bank town of Naalin, where Palestinians and international backers frequently gather to demonstrate against the barrier. Israel says the barrier is necessary to keep Palestinian attackers from infiltrating into Israel. But Palestinians view it as a thinly veiled land grab because it juts into the West Bank at multiple points.

The military says the area where the protests take place is a closed military zone off-limits to demonstrations.

About 400 protesters turned out in Naalin on Friday, the military said. Some of them hurled rocks at troops, who used riot gear to quell the unrest, it added, without elaborating.

Ulrika Jenson, an International Solidarity Movement activist, said troops fired tear gas canisters into the crowd from a hill above.

“Tristan was hit and fell to the ground,” Jenson was quoted as saying in an ISM statement. “He had a large hole in the front of his head, and his brain was visible.” In 2003, another ISM activist, 23-year-old American Rachel Corrie, was crushed to death in Gaza by an Israeli bulldozer as she tried to block it from demolishing a Palestinian home.

The driver said he didn’t see her, and the Israeli military ruled her death an accident.