Israel yesterday rejected demands from Palestinian militants who captured an Israeli soldier to free 1,000 prisoners from its jails and kept up air strikes on Gaza aimed at winning his release.

"His life is at risk if the Palestinian groups do not free the Israeli soldier," a high-ranking official in Palestinian president Mahmud Abbas's office told AFP on condition of anonymity.

"There are Israeli threats against Ismail Haniya through the media," the official said, adding that Abbas had not received any direct messages from the Israeli government.

The militants seized Corporal Gilad Shalit in a raid across the Gaza Strip's frontier last Sunday, sparking a crisis that has sent Israeli-Palestinian relations to new lows.

"Prime Minister Ehud Olmert has reiterated that there will be no deals, that either Shalit will be released or we will act to bring about his release," said Foreign Ministry spokesman Mark Regev, responding to the fresh demands.

A statement from the militants did not specify that freeing the 1,000 "Palestinian, Arab and Muslim prisoners" and ending Israel's Gaza assault would be in exchange for Shalit's freedom.

But a spokesman for the armed wing of the governing Hamas movement, one of the three factions that captured Shalit, said that was what it meant.

The statement from the groups appeared to cast doubt on the hopes of mediators that diplomacy could soon free Shalit, 19.

"We are declaring to the public our just and humanitarian demands," said the statement faxed to news agencies by the Hamas armed wing, the Popular Resistance Committees and Army of Islam.

It repeated an earlier call to free women prisoners and minors in exchange for information on Shalit -- the groups have not said if he is dead or alive.

It said freed prisoners would have to include all Palestinian faction leaders as well as humanitarian cases.

The crisis has piled more pressure on the Hamas Islamist government, already straining under a US-led aid embargo to get it to renounce violence and drop its vow to destroy Israel.

The armed wing of Hamas was one of the three militant groups that claimed responsibility for the soldier's abduction, sparking the worst Israeli-Palestinian crisis since the Hamas government took office in March.

Israel this week arrested scores of Hamas members including ministers and lawmakers and threatened to take further action if 19-year-old corporal Gilad Shalit was not released.

"We view the threats against Haniya as serious," said Mohammed Dahlan, the Gaza strongman of Abbas's mainstream Fatah movement.

"We hope that nothing serious will happen to our brother Haniya or any other Palestinian official," he told AFP.

Israel has launched a vast military operation against the Gaza Strip in retaliation for the June 25 abduction of the soldier during a Palestinian attack on the Israel-Gaza border.

Since the start of the Palestinian uprising in September 2000, Israel has assassinated several top Hamas leaders, including spiritual leader Sheikh Ahmed Yassin and Gaza's former political chief Abdelaziz Rantissi.