Several dozen jeeps and Israeli armoured vehicles entered the area before dawn on Friday and troops have imposed a curfew on the camp, Palestinian security sources said.
An Israeli army spokesman told AFP the operation was aimed at capturing suspected Palestinian resistance fighters.
Israeli occupation forces had officially loosened the noose on the flashpoint towns a week ago after four months of blockade, but troops have staged several raids since.
Palestinians say the continuing Israeli operations in Jenin show the official withdrawal was merely a stunt for propaganda purposes.
Israeli troops also raided the nearby village of Kabatiyah
overnight, seizing two fighters from the Islamic Jihad movement.
The latest Israeli raid on Jenin comes a day after a member of the al-Aqsa Martyrs Brigades, Asaad Salah Khaliliyah, was shot in the head and killed by undercover troops, Aljazeera's correspondent in Jenin reported on Thursday.
Israeli newspaper reports said the assassination was carried out by the Israeli Defence Force's Mistaaravim unit, which uses troops disguised as Arabs.