An ultimatum from Palestinians holding an Israeli soldier has expired. The fate of the soldier, who was abducted from an army base near the Gaza Strip nine days ago, is shrouded in secrecy.

The deadline expired with Israel refusing to meet the demand of Palestinian militants to release more than a 1,000 prisoners in exchange for the kidnapped soldier. Three Palestinian groups, including the military wing of the ruling Hamas party, said they would release no more information about the 19-year-old corporal, Gilad Shalit. However, they said they would not kill him because Islam requires that captives be treated well.

Hamas spokesman Ghazi Hamad says Israel made a grave mistake by rejecting the prisoner exchange.

"You will not get the goal, you will not get the soldier alive by this way. You will increase complication in this situation," Hamad says.

Israeli aircraft and artillery continued to pound militant targets in Gaza including the Islamic university, a Hamas stronghold. Israeli spokesman Ra'anan Gissin says the aim is to pressure Hamas to release the soldier.

"It's based on graduated measures in what can be termed, I would say, full court press. Like in basketball, you know you put pressure on the full court and you apply the right pressure at the right time and you wait for a response," Gissin says.

Despite the threats, diplomatic efforts are continuing. Egypt has been mediating and militants holding the soldier say they are considering a request from Muslim leaders to resolve the crisis peacefully.

In the past, Israel has traded hundreds of Arab prisoners for a handful of soldiers, but that was widely criticized at home and seen as caving in to blackmail. With Hamas in power, Israel has adopted a different strategy and ruled out a lopsided prisoner exchange. Israeli analyst Mordechai Kedar.

"This will deter those who plan kidnapping Israelis from their plans," Kedar says.

Israeli officials say they are determined to show the Hamas-led Palestinian government, that terrorism doesn't pay.