WASHINGTON (JTA) -- An American demonstrator was seriously wounded when Israeli troops and protesters clashed at Israel's West Bank separation fence.

Tristan Anderson, an International Solidarity Movement activist from the Oakland, Calif., area, was hit in the head Friday by a tear gas cannister fired by Israeli troops, according to the Associated Press.

A spokeswoman for the Sheba Medical Center at Tel Hashomer on Friday described Anderson's condition as "life threatening" and said he was "in critical condition, anethetized and on a ventilator, and undergoing imaging tests." Anderson, 38, was on a respirator in stable condition, a hospital spokeswoman said Sunday on condition of anonymity because of the issue's sensitivity.

The Israeli military said that some of the 400 protesters who had gathered at the West Bank town of Naalin had thrown rocks at troops. They also said the area of the protest was a closed military zone off-limits to demonstrations.

The AP quoted another ISM activist as saying that troops fired tear gas canisters into the crowd from a hill above the protest site.

Six years ago, another ISM activist, 23-year-old American Rachel Corrie, was killed by an Israeli bulldozer as she tried to block it from demolishing a Palestinian home. The death was ruled an accident by the Israeli military.