Iraqi government troops have clashed overnight with followers of prominent Shi’ite cleric Mahmoud al-Sarkhi in the holy southern province of Karbala, medical officials say, as the country is roiled by a Sunni-led insurgency.

The clashes erupted after security forces barred al-Sarkhi’s loyalists from praying in a holy shrine in Karbala, witnesses said.

The violence, which continued until early on Wednesday, resulted in an unspecified number of casualties on both sides, according to medics.

Local authorities imposed a curfew in Karbala, about 118 kilometres south of the capital Baghdad, in an attempt to bring the situation under control.

Iraq is already under siege from a rebellion led by the radical Sunni Islamic State in Iraq and the Levant (ISIL, also known as ISIS).

The al-Qaeda splinter group has seized large swathes in Iraq’s Sunni heartland, in the country’s north and the west, since last month.

Earlier this week, ISIL declared the establishment of a caliphate in the areas under its control in Syria and Iraq, fuelling international fears that a regional militant enclave could be emerging.

The rebels’ territorial advances come amid deep rifts in Iraq’s political factions.