The UN agency for Palestinian refugees said Tuesday it had found unexploded 1,000-pound bombs inside schools after Israel pulled troops out of southern Gaza's main city Khan Yunis, AFP reported.

The Israeli army has carried out relentless air strikes and bombardments in Gaza since October 7.

UN agencies led an "assessment mission" in Khan Yunis after Israeli forces withdrew from the embattled city last week, UNRWA said.

It found "significant challenges in operating safely due to the presence of unexploded ordnance (UXOs), including 1,000-pound bombs inside schools and on roads".

"Thousands of internally displaced persons (IDPs) require a range of lifesaving assistance, including health, water and sanitation, and food," it said.

Earlier this month, the United Nations said it would take "millions of dollars and many years to decontaminate the (Gaza) Strip from unexploded munitions".

"We work off the rule of thumb that 10 percent of ordnance doesn't function as designed," UN Mine Action Service chief Charles Birch said in a statement earlier this month.

"We estimate that, to begin the clearance of Gaza, we need around $45 million."