THE return to northern Uganda of Christian fundamentalist rebels, weeks after they fled into neighbouring southern Sudan to escape a military offensive, poses a serious challenge to President Yoweri Museveni.

Analysts said today that renewed attacks by the Lord's Resistance Army (LRA) rebels, who want Uganda run according to the Ten Commandments, also threatened presidential and parliamentary polls scheduled for later this year.

On Friday LRA rebels slaughtered 28 people they had abducted in raids on villages in northern Uganda, and yesterday killed 21 passengers in an attack on an army-escorted vehicle convoy near the Murchison Falls national park.

Four days earlier they engaged the Uganda army in a battle in which 88 people were killed.

``This is not just another episode of sporadic cowardly attacks by disorganised bandits,'' said respected Ugandan MP Gad Gasatura. ``This is a well-orchestrated campaign by an obviously well organised rebel group.

``It is a firm challenge to Museveni's often-praised military credentials and poses a real threat to the proposed elections.''

Presidential and parliamentary elections, Uganda's first since 1980, are due in May and June respectively.

Museveni has repeatedly said the LRA, who have been fighting to overthrow his government since 1987, were a bunch of thugs intent on causing suffering to defenceless civilians to force him to give them jobs in his government.

He insists they are no match for his own ex-guerrilla army, and has repeatedly said he will crush them or push them deep into Sudan, from where they often attack into Uganda.

Analysts disagree. One Western diplomat said: ``The LRA has shown that it is not only capable of serious terrorist attacks. It can engage the Uganda army in tough battles.''

He cited the incident last April in which LRA guerrillas massacred 250 people in a single raid on a northern village, and more recent battles in which they have killed dozens of government soldiers.

The rebels have terrorised large areas of northern Uganda since about 500 of them re-entered Uganda from Sudan last month.

They emerged from the bush to attack isolated villages and abduct young men to fight in their ranks and took women as wives. They cut off people's ears, noses, and lips, accusing them of supporting Museveni.

Recently the rebels have turned up in new battle uniforms, carrying heavy weapons which Uganda says are provided by Sudan.

Khartoum denies this and in turn accuses Uganda of arming the Sudan People's Liberation Army (SPLA), which has fought the Islamist regime since 1983.-Reuter.