Palestinian sources said that an American citizen, in his thirties, had sustained critical wounds during an anti-separation fence protest in the West Bank on Friday, Army Radio reported.

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.

Protesters who were at the scene said that Anderson was standing by the side of the road when soldiers fired at him, and not near the hub of the clash. They added that there was no one in his vicinity that could have been perceived as a threat to the soldiers.

"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 Na'alin, 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 Israel Defense Forces spokesperson's office said the area where the protests take place is a closed military zone off-limits to demonstrations. It added that demonstrators hurled rocks at troops, who used riot gear to quell the unrest.

The IDF said further that the "protesters violated an injunction issued by a major general and were endangering security forces."

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."

A Palestinian protester was also wounded in the leg as a result of live IDF fire.

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.

Meanwhile Friday, protesters gathered at another West Bank village to similarly protest Israel's separation fence. At this protest, held every Friday in Bil'in, some 100 demonstrators clashed with security personnel. Palestinian witnesses reported that five people had sustained injuries as security forces fired rubber-coated bullets at the crowd.