NAIROBI (AFP) -- Recent brief but heavy rains in drought-hit parts of Kenya threaten to worsen the already fragile food situation, with flooding displacing thousands, charity groups warned.

British charity Oxfam International and the Kenya Red Cross Society (KRCS) said the rains will not end the drought and that an urgent boost in humanitarian aid was still critical to avert disaster.

Floods resulting from the rains have displaced more than 3,000 people in parts of northern Kenya and washed away access roads that relief groups depend on to distribute much-needed humanitarian supplies.

"With the coming of the rains in certain areas some people will begin to return to land where they usually graze their livestock -- but this does not mean the end of the crisis," Oxfam said in a statement. "Far from it: initially the rain will exacerbate an already fragile situation," it said. "In fact, in the short term they could make the situation worse by spreading disease and blocking access for food aid."

The KRCS said the rains had displaced thousands of people across Kenya, most in north-central parts of the country, where at least 3,500 people have been forced from their homes.

"As we are speaking now, we do not have access to at least 3,500 displaced people in Isiolo, where heavy rains have also washed away key access roads," Farid AbdulKadir, the head of the society's disaster operations, told AFP.

"As we go along, we expect the rains to displace tens of thousands of people across the country and worsen food shortages," he said.

Kenyan officials said, meanwhile, flooding had forced authorities to evacuate tourists from guesthouses in the Samburu National Park, about 230 kilometers (145 miles) north of Nairobi.

Red Cross officials say at least 50 people have died since December of drought-related conditions in Kenya, home to 32 million people. In addition, tens of thousands of livestock and wildlife have perished.

The World Food Program says it is officially coordinating feeding programs for 3.5 million Kenyans, although last month President Mwai Kibaki said that five million face food shortages across the east African nation.