By Emma Farge

GENEVA (Reuters) -U.N. aid agencies on Tuesday voiced alarm at the scale of the ongoing Israeli military operation in the West Bank town of Jenin, where 10 Palestinians have been killed, saying there were restrictions on medical access.

The operation, which involved drone strikes and hundreds of troops and was one of the largest of its kind in years, entered a second day on Tuesday, prompting the evacuation of thousands of people from a refugee camp.

"We are alarmed at the scale of air and ground operations that are taking place in Jenin in the occupied West Bank, and air strikes hitting a densely populated refugee camp," Vanessa Huguenin, a spokesperson for the U.N. humanitarian office, told a briefing, saying three minors were among those killed. She did not immediately respond to a request for the victims' ages.

Damage to infrastructure caused by air strikes have cut off most of the water and electricity at the camp, she added. The Palestinian Red Crescent previously said it has evacuated around 3,000 people.

The Red Cross said it was "extremely concerned by the alarming intensification of armed violence" in Jenin.

The World Health Organization and medical charity MSF both raised concerns about access.

"Attacks against healthcare including prevention of access to persons injured are extremely concerning," said WHO spokesperson Christian Lindmeier, adding that restrictions put in place by Israeli forces meant first responders could not reach those critically injured within the camp.

Medical charity MSF said that military bulldozers had destroyed roads leading to the camp, making it nearly impossible for ambulances to reach patients.

"Palestinian paramedics have been forced to proceed on foot, in an area with active gunfire and drone strikes," it said.

Israel says the objective of its operation is to uproot Iranian-backed Palestinian factions behind a surge in gun and bomb attacks, as well as preliminary efforts to make rockets.

"Israel ensures that humanitarian assistance is provided and does not apply any limitation on access for medical staff, except in places where the lives of medical staff is at risk due to exchanges of fire," its diplomatic mission in Geneva said in a statement to Reuters.

(Reporting by Emma Farge; Editing by Matthias Williams, Rachel More and Conor Humphries)