U.N. refugee agency officials say the humanitarian situation in Africa's Great Lakes region is deteriorating badly. They say fighting in parts of Burundi and the Democratic Republic of Congo is causing thousands of people to flee their homes.

The refugee agency says thousands of people in eastern Burundi are fleeing their homes because of fighting between government troops and Hutu rebels.

They say more than 5,000 Burundians have arrived in western Tanzania over the past few days, bringing to over 11,000 the number of refugees who have fled to Tanzania since the beginning of the month.

The officials say many of the new arrivals are being housed in an overcrowded transit center run by the refugee agency at Mbuba, close to the border with Burundi.

The normal capacity of the center is 400 people. It now holds almost four thousand people, most of whom are awaiting transportation to bigger camps. The rainy season has begun in the region, which makes transporting the refugees more difficult.

Refugee agency spokesman Ron Redmond said the refugees arriving in Mbuba are exhausted from what they have been through.

"The majority of those arriving are women and children. Many of them are weak and tired. They've walked a long way from their villages," he said. "The majority are arriving with nothing but the clothes on their back."

Mr. Redmond added the refugees are fleeing Burundi because the rebels have told them there will be more fighting.

"They say that they are leaving because rebels are warning them of an impending upsurge in fighting in the region - that's in areas of eastern Burundi," Mr. Redmond went on to say. "They also continue to report reprisals by the Burundian military who are accusing the villagers of complicity with rebels."

But as Burundians flee from the eastern part of their country, refugees from the Democratic Republic of Congo are arriving in western Burundi to escape fighting between the Mayi Mayi, a militia group linked to the central government, and rebels known as Congolese Rally for Democracy.

The refugee agency says so far this week, over 9,000 Congolese have crossed the border into Burundi.