There have been intense exchanges of fire between Israeli forces and armed Palestinian militants in Jenin refugee camp, in the occupied West Bank.
The Israeli military began what appears to be one of its most extensive operations in the territory in years with drone strikes early on Monday.
Eight Palestinians have been killed and 80 injured, health officials say.
Israel said it had “dealt a heavy blow to terrorist organisations”, but Palestinians accused it of a war crime.
The Israeli military said there was no specific timeline for ending the operation, but that it could be “a matter of hours or a few days”.
Jenin has become a stronghold of a new generation of Palestinian militants who have become deeply frustrated by the Palestinian Authority’s aging leadership and the restrictions of the Israeli occupation.
The city has seen repeated Israeli military raids in the past year and local Palestinians have been linked to multiple shooting attacks targeting Israelis.
In 2002, during the second Palestinian intifada, Israeli forces launched a full-scale incursion in Jenin. At least 52 Palestinian militants and civilians and 23 Israeli soldiers were killed during 10 days of intense fighting.
Hundreds of Israeli soldiers were still operating inside Jenin on Monday evening, more than 18 hours after the operation began.
As well as the hum of drones overhead, regular bursts of gunfire and the loud thuds of explosions have been coming from the densely populated refugee camp, which is home to some 18,000 people and is now declared a closed Israeli military zone.
Acrid smoke from burning tyres lit during protests also hung in the air above the city centre. A few young Palestinians were out on the streets, standing close to shuttered shops and staring nervously in the direction of the camp.
The Israel military has cut off telephone communications and the electricity supply to the camp, making it difficult to get an accurate picture of what is happening. Palestinian medics have also been struggling to reach the dozens of injured there.
