Aid agencies are moving 24,000 Sudanese refugees in northern Uganda away from the volatile border area after rebels issued a one-week ultimatum for them to leave.

On Thursday, the Lord's Resistance Army (LRA) ordered all refugees and aid agencies out of the area or face renewed attacks.

We aren't doing it because of the ultimatum

Kris Janowski, UNHCR

The rebel group is still holding four aid workers hostage. They were captured on Monday during an LRA attack on a United Nations camp in which at least 55 people were killed.

The LRA has been fighting the government for 16 years and says it is fighting to rule Uganda according to the Biblical Ten Commandments.

A joint operation by the Ugandan and Sudanese armies to wipe them out earlier this year has only led to even more attacks.

Satellite phone

Kris Janowski, spokesman for the UN refugee agency, UNHCR, said the agency was "racing against time" to help the refugees move south to the Masindi area after the attack on the Achol-pii camp.

"The priority now is to get people out of harm's way," he said.

"We aren't doing it because of the ultimatum."

On Thursday, one of the aid workers from the International Rescue Committee (IRC) told the BBC by satellite phone that the group has been threatened but that so far they had been treated relatively well by their captors.

The LRA say they carried out the attack on a refugee camp in Northern Uganda to avenge the killings of LRA supporters in Sudan.

Revenge

In a statement issued on Thursday, LRA claimed the Ugandan army carried out the attack in collaboration with the Sudanese government and rebels of the Sudan People's Liberation Army (SPLA).

It said workers at the Achol-pii refugee camp had been taken away because the United Nations had not protested at the death of civilian refugees killed by the Ugandan army in Sudan.

LRA leader Joseph Kony (right) is a secretive figure

Speaking to BBC's Focus On Africa programme, one of the hostages said they were exhausted and feared for their lives.

"We've been walking since Monday and some of us have fallen ill," Paul Kalama said on a satellite phone provided by the LRA.

"It's been a long distance and I don't know where we are. But we are still within Uganda."

The attack came only three days after the Ugandan President, Yoweri Museveni, moved to the north of the country to take charge of operations against the rebels.

It was later followed by another rebel attack on Tuesday - in which at least 15 rebels were killed when they took on two army units in northern Uganda.

President Museveni has given permission for religious leaders to try and negotiate with the rebel group.