UN Secretary-General Ban Ki- moon said in Washington on Tuesday that the Israeli attacks on the UN facilities in Gaza are "totally unacceptable and must not be repeated."

Ban, in a statement issued by his spokesperson in response to the Israeli attacks on three UN schools in Gaza, said, "These attacks by Israeli military forces which endanger facilities acting as places of refuge are totally unacceptable and must not be repeated."

"Equally unacceptable are any actions by militants which endanger the Palestinian civilian population," the statement said.

More than 30 people have been killed and 55 others injured in separate strikes on clearly-marked United Nations schools where civilians were seeking refuge from the ongoing violence in Gaza, said John Ging, director of operations in Gaza of the UN Relief and Works Agency for Palestinian Refugees in the Near East (UNRWA).

In the last day, three schools operated by the UNRWA have been hit by nearby Israeli military strikes, the statement said.

"A substantial number of civilians have been killed, particularly in the third strike, and many more have been injured, " Ban said in the statement. "I am awaiting full confirmation of the details of these incidents."

UNRWA's education program has been suspended since the start of Israeli air strikes on Gaza, which Israel says it launched in response to rocket attacks by Hamas militants, on December 27, 2008.

"The locations of all UN facilities have been communicated to the Israeli authorities and are known to the Israeli army," the statement said. "After earlier strikes, the Israeli government was warned that its operations were endangering UN compounds."

"I am deeply dismayed that despite these repeated efforts, today's tragedies have ensued," Ban said in the statement. "Today' s events underscore the dangers inherent in the continuation and escalation of this conflict. I call once again for an immediate cease-fire."

UN staff estimate some 15,000 people have fled to 23 UN-run schools they have turned into makeshift refuges in Gaza. In fighting Tuesday, more than 30 Palestinians were killed in the Israeli air strikes, shelling from tanks and naval bombardments, reports said. Only two of the dead were confirmed as militants.

"There's nowhere safe in Gaza," Ging told reporters. "Everyone here is terrorized and traumatized."

The Israeli attacks on UN schools came as the United Nations intensified diplomatic efforts for a speedy end to the bloodshed in Gaza and southern Israel.

(Xinhua News Agency January 7, 2009)