Recent clashes involving the north and south have raised fears concerning the stability of South Sudan [Al Jazeera]

More than 50 people have been killed in two days of clashes between rebel groups and soldiers in south Sudan's Upper Nile state, an army spokesman said.

Philip Aguer, spokesman for the Sudan People's Liberation Army (SPLA), said on Monday that militia forces loyal
to the rebel leader George Athor clashed with military forces, killing 56 people.

Aguer did not specify which side the deaths were on.

The fighting comes just four months before the region is due to become independent.

The south is expected to secede on July 9 after southerners overwhelmingly voted to declare independence from the north in a January referendum – a vote promised in a 2005 peace accord that ended decades of civil war between north and south.

But a wave of mass killings in recent weeks has raised fears for the stability of Sudan's oil-producing south and the contested Abyei border region.

Internal tensions

Aguer repeated accusations that Sudan's northern government was arming rebel groups to try and disrupt the region ahead of its split and keep control of its oil.

He said the rebel group was linked to the area's Shilluk tribe based near the village of Owach.

"They have received new weapons. We suspect they all acted in co-ordination with Khartoum ... I think things are going to continue escalating," he said.

However, Sudan's dominant National Congress Party (NCP) in the north denied having any involvement.

Rabie Abdelati, an NCP party official, said on Monday: "If we really wanted to go back to war, we would not have signed the Comprehensive Peace Agreement (the 2005 accord) or accepted the referendum.

"We are hoping for a strong south after secession. If the south is not stable the north will not be stable."