* Clashes raise tensions before March elections
* U.S. government condemns violence in the strongest terms
* Kenya sends in paramilitary officers
Fifty-six people have been arrested on suspicion of killing 30 villagers, including women and children, on the coast of Kenya, police said on Saturday.
Friday's violent clash fuelled international concern over security in the east African state ahead of elections next year. Raiders, settled farmers from the Pokomo ethnic group, attacked semi-nomadic Orma pastoralists with guns, machetes and spears.
The two groups have fought for years over access to grazing, farmland and water, but human rights activists blame the latest violence on politicians seeking to drive away parts of the local population they believe will vote for rivals in national elections due in March.
The United States, which sees Kenya as an important ally in a volatile region facing the threat of al Qaeda-linked militants in Somalia, issued a statement roundly condemning the violence. A statement from White House spokesman Jay Carney said:
"The United States condemns in the strongest terms the renewed violence in Kenya's Tana River region ... This latest incident represents a disturbing escalation of the tragic violence witnessed by these communities in August and September."
It added: "With historic elections approaching in March, peace and stability are essential to Kenya's continued progress. The United States urges the people of Kenya to assert their rights through peaceful means, as provided for in Kenya's constitution, so that all Kenyans may realize a secure, democratic, and prosperous future."
After Kenya's disputed 2007 national elections 1,200 people were killed and many thousands more were driven from their homes.
Survivors described Friday's raid. Hamisi Abdul, an Orma, said of the attack by the Pokomo: "They hacked everyone they came across with machetes and spears and shot indiscriminately at us, even as we scampered to seek safety in the bushes. It was confusion. We didn't know which direction they were coming from." Abdul, 27, is in hospital nursing two bullet wounds on his left arm and shoulder.
Police said 11 Pokomo had also died in Friday's violence which they described as a reprisal raid following a series of clashes in August in which more than 100 people died.
They added that the dead among the Orma included six women and 13 children.
"We launched a major overnight man hunt for the attackers and arrested 56 suspects who we believe were involved in the attacks," said Robert Kitur, Coast region deputy police chief.
"Several of them had various body injuries like cuts, confirming that they participated in the attacks."
The suspects were arrested at their homes and a nearby forest where they had gone to hide, he said.
"We also recovered an AK 47 rifle, three rounds of ammunition, hundreds of arrows, bows, spears and machetes. We shall arraign them in court next week to face various charges top among them murder," he said.
President Mwai Kibaki has instructed security forces to prevent further deaths. Police sent an additional team of 200 paramilitary officers to the region to disarm the fighters.
Prolonged trouble on the coast may affect Kenya's vital tourism industry, already damaged by the kidnappings of Western tourists from beach resorts by Somali gunmen and grenade attacks in the port city of Mombasa.