Millions of Shiite Muslim pilgrims beating their chests in mourning thronged the Iraqi city of Karbala Sunday under the protection of thousands of members of the security forces.

The Arbaeen pilgrimage is one of the world's largest religious events and is seen as a major potential target for suicide bombers from the Islamic State jihadist group.

The commemoration of Imam Hussein's death in 680 AD will culminate on Monday but millions were already packing the city hosting the shrine of the Prophet Mohammed's grandson.

Nusayyef al-Khattabi, who heads the Karbala provincial council, said he expected the total number of visitors over several days to range "between 17 and 20 million".

Among them are an estimated three million foreigners, mostly Iranians who started crossing the border days ago.

"We are on maximum alert," Staff Major General Qais Khalaf Rahaima, the head of the security command responsible for the area, told AFP.

Many in the sea of black-clad devotees swarming the shrine walked days to reach Karbala, sometimes from cities as far afield as Basra, about 500 kilometres (300 miles) away by road.

Baghdad and much of the country south of the capital come to a standstill in the days preceding Arbaeen, as several major motorways are reserved for pilgrims on foot on one side and authorised vehicles on the other.

Arbaeen, which means "forty" in Arabic, is an observance that peaks on the 40th day after the anniversary of Hussein's death, but the pilgrimage takes place over several days running up to it.

"Around 24,000 members of the army and police have been involved in the implementation of a security plan over three weeks," Rahaima said.

Tens of thousands of Iraqi forces are battling the Islamic State group in and around Mosul, a large northern city and the jihadists' last major urban stronghold in Iraq.

Since the previous edition of Arbaeen in December 2015, their self-proclaimed "caliphate" has been unravelling and the jihadists are expected to increasingly turn to spectacular one-off attacks on symbolic targets.

Karbala, which lies about 80 kilometres (50 miles) southwest of Baghdad, faces the desert of Anbar, a vast province which was until recently an IS bastion and where jihadists still carry out frequent attacks.

Source: AFP