Nairobi - Militaries in north and south Sudan are engaged in an arms race that risks plunging the nation back into civil war, a study said on Thursday.

The north and south fought a two-decade civil war that ended with a 2005 peace deal. But relations remain tense and the agreement faces important tests soon -- national elections next year then a referendum on southern independence in 2011.

On top of that, a surge of ethnic clashes in the south have killed more than 1,200 people this year, stoking fears of more insecurity in the remote and underdeveloped region.

Southern officials accuse their former civil war foes from the north of arming rival tribal militia to destabilise their region before the election and referendum. Khartoum denies it.

Some 2 million people died and 4 million fled between 1983 and 2005 as the Muslim north and mostly Christian south fought over differences in ideology, ethnicity and religion.

The report said China and Iran continued to be the main source of weapons that were adding to turmoil in the country.