CAIRO -- A U.S. drone strike in Afghanistan killed a son of an Egyptian-born militant cleric imprisoned in the United States for plots in the 1990s to blow up New York City landmarks, an Islamist group said Saturday.

Egypt's Gamaa Islamiya, or Islamic Group, posted on its website a notice mourning the death of Ahmed Abdel-Rahman, the son of Sheik Omar Abdel-Rahman, known as the "Blind Sheik", who is now serving a life sentence in the United States.

The 73-year-old sheik was the spiritual leader of the Gamaa, as well as of the men convicted in the 1993 World Trade Center bombing.

Ahmed's path to militant jihad began at the age of 15 when he went with his elder brothers to Afghanistan to fight against the Soviet Union, which occupied the country for around a decade until the late 1980s.

He was 37 years old when he died, having never returned to Egypt, his family said.

His elder brother, Mohammed, was in Afghanistan with him in the 1980s during the fight against Soviet forces.

"My feeling is of happiness that he died on the path to God as a martyr," Mohammed said, speaking to The Associated Press in Cairo. "He was my friend and my brother in jihad."

Mohammed said that both he and Ahmed left Afghanistan after the 1989 Soviet withdrawal for neighboring Pakistan. He said his brother lived in Pakistan's border region of Waziristan among the families of militants killed in battle until Pakistan began repatriating Arab fighters. Ahmed then fled to Yemen, fearing that if he was sent back to Egypt he would be imprisoned and tortured.

In 2001, when the United States went to war against the Taliban in Afghanistan, Ahmed returned to battle U.S. and NATO forces, his family said.

"The same reasons for fighting the Soviet occupation of Afghanistan were the same reasons he wanted to fight the U.S. occupation of Afghanistan," Mohammed said. "It was his right to defend himself and liberate Muslim lands from occupation."

The family said it is not clear when Ahmed was killed or where. The last two days have seen an uptick in U.S. drone attacks in Pakistan close to the Afghan border.

The Gamaa Islamiya was a militant organization and fought the regime of then President Hosni Mubarak in a bloody insurgency in the 1990s, seeking to establish an Islamic state in Egypt.

The group eventually declared a unilateral cease-fire and has operated more openly since Mubarak's overthrow in an uprising earlier this year.

However, the group, which advocates a strict interpretation of Islamic law, was barred this year by the government from forming a political party.