Army spokesman Lieutenant Paddy Ankunda said the rebels, belonging to the Lord's Resistance Army (LRA), attacked the town of Bobi, 320 kilometres (200 miles) north of Kampala, on Sunday.

Unholy war

The LRA says it wants to rule Uganda under the Biblical 10 Commandments Leader Joseph Kony keeps numerous "wives", many of them abducted girls kept as sex slaves The group is notorious for abducting children to swell its own ranks, said to be about 4,000-strong

The rebel group announced at the weekend that it was declaring a unilateral ceasefire, following an offer of peace talks by President Yoweri Museveni.

The army responded by saying conditions set by President Museveni must first be met before there is a truce.

President Museveni first made the offer of a truce when he wrote to LRA leader Joseph Kony in July.

As a condition for peace talks to begin, the rebels would have to assemble in specific areas in both southern Sudan and northern Uganda where they could be monitored by the security forces.

"We shall not allow them to stay in inaccessible areas... because doing that would mean that they intend to continue with the war," said Mr Museveni.

The one-week ceasefire is aimed at allowing them to assemble.

Caution

Peace mediator Norbert Mao has cautioned the army against being inflexible.

"These conditions being pushed by the army and the government and Uganda can scuttle the peace process," he warned the BBC's Focus on Africa. He said it was not clear who was carrying out the ambushes and he said the government needed to be flexible if it was determined to pursue peace.

The LRA has been fighting the government since 1987, operating mainly in northern Uganda, where an estimated 500,000 people have been displaced by the fighting.