Updated

Gunmen killed a Sunni imam and his son in the mostly Shiite city of Basra in southern Iraq as they were leaving a mosque after Friday prayers, police said.

The attack occurred one day after Iraq's top Shiite cleric, Grand Ayatollah Ali al-Sistani, had tried to curb sectarian violence in the region by ordering all Shiite mosques to close for three days in a town near Basra where a local Sunni Arab leader had been assassinated.

CountryWatch: Iraq

In Friday's attack, three gunmen killed Sheik Khalil Ibrahim, a Sunni imam of the al-Khudairi mosque in the Ashar area of central Basra, and his son as they were leaving the building after Friday prayers, said police Capt. Mushtaq Kadhim.

Al-Sistani had issued the edict for mosques in Zubayr to be closed Friday, Saturday and Sunday after gunmen killed Sunni imam Sheik Khaled Ali Obeid al-Saadoun and two of his associates Wednesday as they left a mosque there after evening prayers. Al-Saadoun also had served as the local leader of the Iraqi Islamic Party, a Sunni Arab political group.

Zubayr is about 13 miles southwest of Basra, the provincial capital where most of the 8,000 soldiers that Britain has in Iraq are based.

Southern Iraq has long been much less violent than Baghdad and western Iraq where Sunni Arab-led insurgents and Al Qaeda in Iraq launch frequent attacks against Iraqi civilians and U.S. and Iraqi forces. But al-Sistani hasn't always been able to control growing anti-coalition fervor among Shiite radicals.

Last Saturday, a British military helicopter crashed in Basra, killing the five-member British crew. Apparently downed by a missile or rocket, it hit a two-story house. A crowd of Iraqis cheered and threw stones at British forces who raced to the scene to seal off the area.

Last month, the body of a Sunni lecturer in the Basra Technical Institution, Salah Aziz, was found by police in Basra, a day after he was seized by gunmen.