Police are struggling to restore order in Kenya, amid a wave of violence linked to December's disputed presidential election.
Riots are continuing in the towns of Naivasha and Nakuru in the Rift Valley, where dozens of people have been killed in five days of ethnic violence.
Violence has also erupted in Eldoret and further west in Kisumu, both scenes of earlier bloodshed.
Analysts warn a cycle of violence is emerging amid the political impasse.
They say this takes the pattern of attacks followed by reprisal attacks.
The national death toll since the elections is now about 800.
Members of President Mwai Kibaki's Kikuyu tribe have been fighting with Luos and Kalenjins who backed his rival Raila Odinga in the election a month ago.
Mr Odinga accuses Mr Kibaki of stealing the vote and has refused to recognise the result.
Much of the weekend's violence centred on Nakuru and Naivasha.
The BBC's Adam Mynott in Nairobi says Naivasha, which witnessed brutal scenes on Sunday, is once again a battleground between rival ethnic communities.
Here, many of the attacks are said to have been carried out by Kikuyu clan members in retaliation for earlier attacks.
In one of Sunday's worst incidents, 19 Luo people were burned to death in a house they sought refuge in, after being chased through a slum by a gang of Kikuyus, police said.
Fourteen people were killed overnight.
On Monday, there were tense stand-offs in the town between the rival gangs. Outside the Lake Naivasha Country Club hundreds of men from Kikuyu and Luo sides are being kept apart by only a handful of police officers, who are firing live rounds into the air.
"We want these Luos to go home," a Kikuyu protester holding a plank of wood told a Reuters reporter in Naivasha.
"They chased and killed our people. Now we want the same thing to happen to them."
Earlier there were riots in the western opposition stronghold of Kisumu, as Luos demonstrated against the violence in Nakuru and Naivasha. Two people were reported killed, but calm was later restored.
There has also been violence and houses have been burned in Eldoret in the Rift Valley, and Kakamega in western Kenya.
Police say they have arrested 159 people in Naivasha and Nakuru over the past hours, and a further 95 people in Nairobi. Separately, two Germans were hacked to death with machetes at a resort south of Mombasa, in an incident involving a robbery and apparently unconnected with the ethnic violence.
There is mounting international concern at the spiralling violence.
On Monday, European Union foreign ministers urged Kenya's politicians to work to find a solution or risk a cut in EU aid.
While President Kibaki says he is open to talks, he has refused to countenance Mr Odinga's demand for fresh elections.
The former UN secretary general Kofi Annan has been trying to mediate a solution between the two sides. After meeting Mr Odinga on Sunday, he was due to meet Mr Kibaki again on Monday.
But the UK's visiting minister for Africa, Mark Malloch-Brown, who met key players in meetings on Monday, said the challenge was great.
"Negotiations are becoming more and more difficult because the level of anger at the two sides is just growing exponentially," he told reporters, according to AP.
"The two sides are very far apart at this time."