Fear of rebel attacks has forced many from their homes

The encounter happened after about 100 members of the Lord's Resistance Army (LRA) crossed the border from Sudan, a Uganda army spokesman said.

He said no troops had been killed in the clash, 80km (50 miles) from Gulu.

The LRA is accused of massacring over 200 civilians at a refugee camp near Lira last month - the worst atrocity in its 17-year insurgency.

Correspondents say that, although the army often claims it is winning the war against the LRA, many Ugandans are sceptial because the rebels continue to launch sudden attacks on poorly defended civilian targets.

Sustained assault

"One hundred or so rebels crossed over from southern Sudan on Friday but came into contact with our forces on Saturday," army spokesman Shaban Bantariza told Reuters news agency.

"We subjected them to a sustained assault and killed 55 of them."

He said the battle took place in Bibia, north-west of Gulu, and that the rebels were being led by deputy chief Vincent Otti, who survived the attack.

Earlier this month, Sudanese rebels said they had launched a major offensive against the LRA, who have launched attacks from southern Sudan.

The Sudanese groups - including the main SPLA rebel group - say they are retaliating for LRA atrocities committed in southern Sudan itself.

Uganda has accused the Sudan government of backing the LRA.

Despite this, Khartoum has given the Ugandan army permission to pursue the LRA on Sudanese territory.