GAZA CITY -- A jailed senior Hamas leader disowned his son on Monday after the young man admitted to having spied on the Islamist group for Israel and playing a major role in the arrest of senior militants.

"I, Sheikh Hassan Yussef... my wife, sons and daughters announce that we have completely disowned the man who was our oldest son and who is called Mosab," he said in a statement.

The decision was taken following "the man who is called Mosab's apostasy towards God and his prophet... his betrayal of Muslims, his cooperation with the enemies of God and the damage he caused to our people and our cause."

Last week, Israel's Haaretz daily reported that Mosab Hassan Yussef, 32, was a top informer for Israel's Shin Bet internal security agency and was known by the codename "The Green Prince."

The article was based on extracts of a book, "Son of Hamas", co-written by Yussef, who converted to Christianity 10 years ago and now lives in California. The book is set to be published in the United States this week.

Haaretz said Mosab was crucial in the arrests of Ibrahim Hamid, a Hamas military chief in the West Bank, and Abdullah Barghuti, the bomb maker behind an infamous 2001 suicide attack on a Sbarro restaurant in Jerusalem.

Yussef reportedly worked for the Shin Bet at the height of the 2000 Palestinian intifada, or uprising, when Hamas carried out dozens of deadly suicide bombings in Israel and Israel waged an all out war on the group.

The elder Yussef -- a senior Hamas leader in the West Bank who was arrested in September 2005 and is still being held in an Israeli jail -- had earlier denied his son was ever an active member of the group.

"From 1996, when he was 17 years old, (Mosab) faced blackmail and pressure from Israeli intelligence and, when he revealed his situation at that time, the sons of the movement were warned about him," he said in an earlier statement.

Hamas has also said the elder Yussef worked entirely in the public political wing of the movement. He was elected to parliament in 2006.