NAJAF, Iraq (AP) — Iraq's most powerful Shiite Muslim cleric on Monday condemned what he described as Israel's "ugly crime" in killing Sheik Ahmed Yassin, the founder and spiritual leader of the militant Palestinian group Hamas.

"We call upon the sons of the Arab and Islamic nations to close ranks, unite and work hard for the liberation of the usurped land and restore rights," Grand Ayatollah Ali al-Husseini al-Sistani said in a statement released by his office in the Shiite holy city of Najaf.

"This morning, the occupying Zionist entity committed an ugly crime against the Palestinian people by killing one of their heroes, scholar martyr Ahmed Yassin," the statement said.

Yassin and seven others died in a missile strike from an Israeli helicopter as he left a mosque in Gaza City early Monday.

Al-Sistani has major influence in Iraq's political process. On several occasions, he has forced the U.S.-led coalition that is running the country to drop or revise plans linked to a power handover to Iraqis by July 1.