Addis Ababa - Heavy rain, swirling waters, mud, silt and marsh combined Wednesday to hamper frantic efforts to reach thousands of villagers marooned by deadly flash floods in southern Ethiopia, officials said.

The elements, along with the reluctance of pastoralist herders to leave their surviving cattle for higher ground, frustrated the delivery of the first overland relief supplies that reached the remote region on Tuesday, they said.

Delays in the distribution of food, water, medicine and shelter stoked fears the death toll would rise in the devastated area where at least 364 people were killed when the Omo River burst its banks on August 13, displacing some 10,000.

"Our teams are still struggling to reach the affected areas, but the marsh and silt created by the floods are preventing us," said Petros Gebre, the deputy police chief of the Southern Nations, Nationalities and People's state.

"And, aid distribution is becoming problematic as about 3,000 people who have declined to be relocated are unreachable by land," he told AFP by phone from Jinka, about 800 kilometers (500 miles) southwest of Addis Ababa.

"We are providing them with aid drops of aid from helicopters but it's not clear how long we can do this," Petros said, calling the situation a "logistical nightmare".

Despite assurances that the government would take care of their livestock while they are relocated to safer ground to facilitate relief distribution, the 3,000 herders are refusing to leave, he said.

"Even though we have promised that they can return to their cattle when the water levels decrease, they have refused to move," Petros said.

He added that the search teams were yet to recover an unknown number of bodies of drowned victims after villagers reported spotting them on the marshlands on the Omo River delta on Monday.

Floods caused by unusually heavy seasonal rains have battered huge portions of southern, eastern and northern Ethiopia since the beginning of the month, killing at least 626 nationwide and affecting 118,000 people, many of whom have been left homeless.

The Ethiopian News Agency reported Wednesday that 8,000 people had been displaced in Gode Zone, about 970 kilometers (600 miles) southeast of the capital, by floodwaters from the Wabi Shabelle River.

State TV agency said that thousands more were forced to flee to higher ground in the Gambella region when Baro River broke its bank, flooding farmlands.

"More than five villages in four districts in Gambella regional state were flooded when Baro River overflowed its banks displacing more than 7,000 people destroying their residential areas," the television added.

Concerns about the spread of water-borne diseases are also growing as rain continues to pound the Ethiopian highlands.

The downpours have pushed water levels at at least three critical dams to the breaking point, and authorities began controlled releases from one of the facilities, the Gilgel Gibe dam on the Omo River, on Monday.

Officials said local authorities planned to start releasing overflowing water from Koka dam on the Awash River that has flooded in the east, and the Tise Aby on the Blue Nile in the north.

Ethiopian Electric Power Corporation officials said water would be released from the dam starting 6:00 am (0300 GMT) on Thursday.

"Dykes they have built in the area are capable of holding the amount of water that will be released," the firm's spokesman Sendeku Araya told AFP.

"There is nothing to panic about as it is going to be monitored closely and every preparation has been made for any eventuality," he added.

The United Nations has made an urgent appeal for 5.82 million dollars (4.54 million euros) for the thousands who have been displaced as well as for the rehabilitation of infrastructure in the flood-hit eastern town of Dire Dawa, where 254 people were killed on August 6.

Forecasters have warned that six areas in the north, west and south of the country will likely face further flood threats from the rains that are expected to continue until the end of the wet season in September.

Ethiopia, home to some 70 million people, has faced heavy floods and droughts in recent years.