An American injured last week during a demonstration near the West Bank village of Naalin remains in critical condition, still heavily sedated but breathing on his own, a hospital official said Monday.

Tristan Anderson, 37, was struck in the head Friday by a tear gas canister fired by an Israeli soldier during a Friday afternoon protest over the construction of an Israeli security barrier. "A full investigation will ensue," the Israel Defense Forces said in a statement.

The Californian has been removed from a respirator, and a spokesman for Tel Hashomer hospital in Tel Aviv said he was "semi-conscious" after days under full anesthesia. Anderson's associates and hospital and other officials said he was able to lift fingers on one hand in response to a voice command.

Jonathan Pollat, a member of an Israeli group also active in the Naalin demonstration, said doctors at the hospital told him they would not be certain about any long-term impairment or possible brain damage until more tests are done.

Anderson's parents arrived in Israel today, but through Pollat declined to comment.

The barrier -- a high concrete wall in some places; a combination of wire fencing and roads in others -- surrounds much of the occupied West Bank. While it adheres in some places to the "Green Line" boundary that marks Israel's border before its 1967 war with surrounding Arab states, in others it pushes into the territory. Israel says security concerns dictate the route of the barrier, and credit it with a drop in suicide bombings. Palestinian farmers and residents say the route amounts to a land grab and that the barrier impedes movement and commerce.

In recent months, protests against the barrier have broken out on a near weekly basis around Naalin. Four Palestinians, including two children, have been killed in the area since the summer, according to Sarit Michaeli, spokesman for the Israeli peace group B'Tselem, and dozens have been injured. The IDF says 73 border police officers and soldiers have been hurt by rocks and other objects thrown by Palestinian protesters in the area.

Anderson attended the demonstration as part of the International Solidarity Movement, a group that has clashed intermittently with Israeli authorities since it began operating in the West Bank and Gaza Strip several years ago. Two of its members have been killed -- American Rachel Corrie and British citizen Tom Hurndall, both in the Gaza Strip -- and another protester suffered serious wounds. Corrie was killed by an Army bulldozer in what Israeli officials concluded was an accident; Hurndall was shot by an Israeli soldier who was convicted of manslaughter.

Israeli officials have accused the group of blurring the line between legitimate protest and involvement with those intent on violence. A wanted member of the armed Islamic Jihad organization, for example, was arrested at the group's offices in Jenin in 2003.

Adam Taylor, a spokesman for the organization, said the group is committed to nonviolence and sends volunteers to disputed areas such as Naalin "to try and lessen the risks for the Palestinians," working on the assumption that Israeli army and police forces will temper their response to demonstrations if they know that foreign nationals are present. There are currently about 30 ISM volunteers in Nablus, Hebron and other places, he said.

A spokesman for the U.S. Embassy, Stewart Tuttle, said U.S. officials are expecting more information from Israeli officials.

"We are awaiting a response from the IDF on the circumstances before we decide on next steps," Tuttle said.