Darfur - South Sudan's army and militiamen have exchanged heavy gunfire in the town of Malakal, according to local officials and eyewitnesses.

It reportedly involves the southern army and a militia led by Gabriel Tang, who was backed by Khartoum during Sudan's 21-year north-south civil war.

Fighting between South Sudan's army and elements in the Tang militia killed 150 people in Malakal in 2006.

The north-south conflict cost an estimated 1.5 million lives and ended in 2005 with the setting up of an autonomous secular government in the south.

He said southern army soldiers from a special joint unit of both northern and southern troops stationed in Malakal under the peace accord were involved in the fighting.

But it was not immediately clear if any northern forces had joined in the clashes.

South Sudan Information Minister Gabriel Changson Cheng said the fire-fight had been on and off all day and there was no official confirmation of any deaths as yet.

The confrontation came as Sudan's President Omar al-Bashir made a rare visit to the south's capital.

The International Criminal Court will announce on 4 March whether it is to indict him for alleged war crimes committed in the separate conflict in the western region of Darfur - a move correspondents fear could worsen the fighting in Darfur and even drag South Sudan back to war.