Some 400 Palestinians and 150 foreign activists, including Israeli pacifists, took part in the protest on Friday in the village of Masha, southeast of the northern West Bank town of Qalqiliya.
Israeli troops threw teargas and then opened fire at the crowd which was tearing down a metal gate built into the wall, witnesses and security sources said.
Live bullets were used against the protesters and two of them were wounded as a result, Israeli military sources confirmed.
They said the troops fired warning shots to disperse the crowd and then fired at protesters' legs, according to rules of engagement, to stop them from making a hole in the gate.
The two wounded activists were evacuated to Bellinson hospital near Tel Aviv, in northern Israel.
The Israeli pacifist, named as Gil Naamati, was seriously wounded and had to undergo an operation, a hospital spokesman said. The American woman, who was not identified, was lightly hurt.
"By opening fire at demonstrators, Tsahal (the Israeli army) overstepped its boundaries," Israeli left-wing MP Yossi Sarid told public radio.
"By opening fire at demonstrators, Tsahal (the Israeli army) overstepped its boundaries"
leftwing Israeli MP
Despite an international chorus of criticism against the wall, which the US administration calls a "problem" as it juts deep inside the West Bank, Israel says it is needed to prevent Palestinian assailants from infiltrating its territory.
The apartheid wall is due for completion in 2005 and will stretch some 700km.
Palestinians say it pre-empts the borders of their future state as its path does not strictly follow the West Bank occupied by Israel in 1967.
On 21 October the United Nations General Assembly passed a resolution demanding that Israel stop the wall's construction at once.
And on 8 December the international body asked the International Court of Justice in the Hague to give an opinion on the barrier's legal implications.