Nairobi - Aid workers said Wednesday they estimated that around 20,000 people had fled across the border and needed support after a recent upsurge in deadly clashes.

Clashes in northern Kenya between rival ethnic groups in recent weeks have forced tens of thousands of people to flee into neighbouring Ethiopia, the UN has said.

"Conflict between the Borena and Gabra clans in northern Kenya has displaced tens of thousands of people," the UN Office for the Coordination of Humanitarian Affairs said in a report released Tuesday.

The majority of those who have crossed into Ethiopia were living with host families, UN added.

Food for 15,000 people has been sent to the area, along with plastic sheets and household items for some 3,000 people, it added.

Fighting over land grazing rights in Kenya's remote northern Moyale region killed at least 18 people last month after two days of intense violence between men armed with automatic rifles and machetes.

The region was hard hit by severe drought in the Horn of Africa last year, exacerbating tensions over land in the area, and sparking tit-for-tat cattle raids.

Clashes between rival cattle herding pastoralists in the region are common, with herders often carrying guns to protect their animals, but the recent fighting has been unusually heavy.