JUBA, Sudan, Feb 24 (Reuters) - South Sudan's army and militiamen traded heavy gunfire on Tuesday in the south Sudan town of Malakal, eyewitnesses and southern army officials said.
The fighting was between the southern army and members of a southern militia headed by Gabriel Tang, who was backed by Khartoum during Sudan's long civil war between the north and south, a senior commander from the south's army said.
"This (fighting) is because Tang arrived yesterday in Malakal. The U.N. tried to persuade him to leave but he refused," James Hoth told Reuters.
Hoth said the fighting had been heavy, but it was not yet known whether anyone had been killed or wounded.
Fighting between south Sudan's army and elements in Tang's militia killed 150 people in Malakal in 2006 and was a major threat to a fragile north-south peace deal signed in 2005.
A witness sheltering from gunfire said there had been two separate outbreaks of gunfire and explosions.
"There's been heavy shooting this morning from about 8 a.m. There have also been big explosions ... there are tanks on the streets," said the witness, who declined to be named.
After the 2006 fighting the south's President Salva Kiir issued an arrest warrant for Tang and he was barred from Malakal, Hoth said.
The southern army soldiers involved in the fighting are from a special joint unit of both northern and southern forces that control the south's towns and oil fields under the peace accord, Hoth said.
The northern army contingent contains former members of Tang's militia, Hoth said, but it is unclear whether they are involved in Tuesday's fighting.
Some 2 million people were killed in Sudan's north-south war and another 4 million displaced from their homes. (Reporting by Skye Wheeler; editing by Elizabeth Piper)