The announcement came as a Hamas military court sentenced a Palestinian man accused of assisting Israel's secret service to death by firing squad, security sources said.

Ehab Al-Ghsain, spokesman for Gaza's interior ministry, said some of the suspected collaborators were accused of aiding Israel in a late 2008 war in which 1,400 Palestinians and 13 Israelis were killed.

"The phenomena (collaboration) is small but we have arrested many," Abu Abdallah Lafi, a senior official in Hamas internal security service, told a news conference. He would not say how many people were detained but said they included some women.

Ghsain asserted the suspects posed "a real danger to the unity of the people and their resistance" against Israel, which has sealed off the narrow coastal enclave by land, sea and air.

Hamas security organs had obtained "serious confessions and uncovered many collaborators who stood behind assassinations of some leaders of resistance and implemented policies of the enemy's intelligence service against our people," Ghsain said.

Some of the suspects had planted bombs at training camps and government offices that caused Palestinian casualties, while others had helped to facilitate Israeli raids into Gaza and assassinations of militants, he said.