Grand Ayatollah Ali al-Sistani, the most senior Shia cleric in Iraq, unexpectedly returned to his homeland on Wednesday after nearly three weeks overseas during which anarchy has rapidly taken hold.

As he arrived in the southern port city of Basra after being treated in London for a heart condition, Mr Sistani's spokesmen called on Iraq's majority Shia community to march to the embattled holy city of Najaf to end three weeks of fighting.