The resistance fighters ambushed a number of occupation soldiers who are now besieged inside one of the buildings in Jenin’s old city, Aljazeera’s correspondent reported from the scene.
There were no immediate figures for casualties from the clashes.
The fighting erupted when the Israeli occupation forces, backed by a number tanks and armoured vehicles, raided the city again on Friday morning, following four days of curfews and repeated incursions.
Jenin was the focus of international attention in April 2002 when the United Nations ordered a team of investigators to go and check out allegations of war crimes after an israeli invasion and siege.
More than 50 residents were killed during the siege, many of them women and children. Ariel Sharon refused to allow the UN inspectors access to Jenin where 300 homes had been bulldozed to the ground by the Israeli army.
Israeli occupation forces also raided Palestinian territories in Beit Hanoun, in the northern Gaza Strip after an overnight break to uproot more foliage in the area from where a rocket was launched into Israel.
Israeli bulldozers, accompanied by several tanks, set out to flatten trees and level farms to deny cover to Hamas rocket squads.
Amid Palestinian fears of a major invasion, a military source said the "very small force" would return to Israeli territory once the mission was completed.
Troops found the rocket launcher 15m from a manned Palestinian police post, Israeli security sources said.