Gordon Brown has urged Kenya's political leaders to talk in a bid to end the violence gripping the country.
"The violence must be brought to an end," the UK prime minister said, following the death of at least 120 people amid disputed election results.
Mr Brown said he had spoken to Kenyan President Mwai Kibaki and opposition leader Raila Odinga to push for peace.
The Foreign Office is urging the estimated 30,000 Britons visiting or working in Kenya to stay indoors.
Mr Brown said the Kenyan politicians had an obligation to find a solution to end the violence in their country.
"I want to see the possibility explored where they can come together in government," he said.
He added: "There has been criticism of the election procedures. I think it is important all sides must recognise that by working together we can make progress.
"But the first priority is that the violence is brought to an end. It is unacceptable that lives are being lost."
Mr Kibaki was officially re-elected president in the election but Mr Odinga has said publicly that he was robbed of victory by voting fraud.
EU election monitors have described the poll as "flawed", saying it "fell short of international standards".
British tourists currently in Kenya have been told by the Foreign Office to avoid the centre of Kenyan capital, Nairobi, and warned against all but essential travel to some districts in Mombasa.
Many of them are on safari or staying in beach resorts close to Mombasa, where there have been violent clashes.
British teacher Artie Smith, who lives 15km outside the town of Nakuru, where there have also been clashes, said the entire community can feel the tension in the air.
"It is eerily quiet right now and everyone just feels very tense and everyone is very nervous," said the 26-year-old from Woking, who has lived in Kenya since August 2005.
Mr Smith said he felt fairly safe within the compound of the international school where he teaches and had sufficient supplies for the time being.
Mr Odinga (left) has accused Mr Kibaki of electoral fraud
He said he and some friends might venture into town on Wednesday to restock ahead of planned political demonstrations in Nairobi on Thursday, which he believes will bring a fresh wave of violence.
Mr Smith said that while he knew the election would be a tight race and expected some small skirmishes as a result, the reaction of the losing side caught him off guard.
Mr Smith said there was no sense of any increased safety risk for foreigners, adding that local tribal affiliation seemed to be playing a role in determining who was targeted.
"The local people who work with us seem worried about that and people are being checked for their identity card for which tribe they belong to," he said.
Kenyan David Seda, who lives and works in London, flew out of Nairobi yesterday after visiting his parents outside of Kisumu town.
He said just negotiating a driver to take him past a string of roadblocks on the first leg of his journey to town was "very frightening".
"And every time we approached a roadblock they were in flames and you would see about two-hundred people at each roadblock," he said, adding that people had to be bribed at every point in order to let him proceed.