Youths hurled stones at a force the army said it ordered into northern Gaza after resistance fighters fired rockets and mortars at Jewish settlements and an Israeli town to avenge the assassination of Hamas leader Abd Al-Aziz al-Rantisi.
Tension in Gaza has risen since Israel's killing of al-Rantisi in a helicopter strike on Saturday. Hamas vowed to carry out "100 retaliations".
Medics said four Palestinians, aged 17,18, 19 and 21, were killed by army gunfire. At least 25 other Palestinians were wounded in two separate confrontations, and two were listed in critical condition.
Israeli military sources could not confirm either death, but said troops fired at a Palestinian who climbed on to an armoured vehicle and at Palestinians who shot at the troops, threw grenades, petrol bombs and detonated explosives.
Five soldiers were lightly wounded in the confrontations, including one from an explosive device, the sources said.
Since Sunday, at least nine Israelis have been wounded in
mortar bomb and Qassam rocket attacks on Gaza settlements and the southern Israeli town of Sderot, the army said.
Tension has built in Gaza since Israel killed al-Rantisi in a missile strike less than a month after Hamas spiritual leader died in a similar attack.
Palestinians are also fuming at Israel over a unilateral "disengagement" plan, approved by US President George Bush last week, that would mean a withdrawal from the Gaza Strip, but a stronger Israeli hold on big chunks of the West Bank.
Both territories were captured in the 1967 Middle East war and are wanted by Palestinians for a future state.
Earlier, Israeli troops imposed a day-light curfew on Silwad village near the West Bank city of Ram Allah, and then performed house to house searches, arresting dozens of men.
Hamas wants to retaliate for
the killing of al-Rantisi
Aljazeera's correspondent in the West Bank, Walid al-Umari, reported that house to house searches continued into the early hours of Tuesday morning.
"Soldiers smashed much of the contents of the houses they searched, arresting many men and transferring them to a military camp in a nearby settlement," said the correspondent.
"It seems occupation forces are looking for Ibrahim Hamad, leader of the Izz al-Din al-Qassam Brigades in the village," he added.