Diplomatic efforts are continuing in Kenya to end a political crisis after last week's disputed presidential poll.
Jendayi Frazer, the top US envoy for Africa, has met opposition leader Raila Odinga in Nairobi and is to see President Mwai Kibaki shortly.
The opposition say Mr Kibaki cheated to win a second term on 27 December.
Post-election violence has claimed 350 lives in the east African country and at least a quarter of a million people have been displaced, the UN believes.
Some have been housed in makeshift camps while others have sought refuge in police stations or churches.
Anti-government protests have fizzled out and the president has said he may accept opposition demands for a fresh election, but only if ordered by a court.
But Mr Odinga's Orange Democratic Movement (ODM) has said it will not go to court because it has no confidence in its rulings.
Calls for calm
The US would not comment on the meeting between Ms Frazer and Mr Odinga, which lasted two and a half hours, but an ODM representative said it had been constructive.
Jendayi Frazer met Raila Odinga over breakfast on Saturday
Mr Odinga had called for international mediation and for the election to be held over again, the representative added.
Mr Kibaki has said he will not accept foreign mediation in the dispute, though he has spoken on the phone to a number of international leaders.
UN Secretary General Ban Ki-moon earlier urged calm in separate telephone conversations with Mr Kibaki and Mr Odinga.
UK Foreign Secretary David Miliband urged Kenya to let the head of the African Union, Ghanaian President John Kufuor, play a mediating role in the crisis.
On Friday, French Foreign Minister Bernard Kouchner said he believed the election had been "rigged".
Francois Grignon, the Africa director of the International Crisis group, said what was needed was a coherent plan by all interested parties, not just a series of visits.
"International efforts... have to come together on a joint strategy, and the reputation of visits by high-level officials is not necessarily going to deliver a solution," he told the BBC's World Today programme.
The talks in Nairobi come amid warnings by UN officials that a humanitarian crisis was worsening across Kenya.
The regions worst hit are western Kenya and the Rift Valley.
There is plenty of food in the country but trucks have been unable to deliver it because of vigilante violence on many roads, the BBC's Adam Mynott reports.
The UN World Food Programme (WFP) is providing supplies for 100,000 people in the northern Rift Valley.
"We need supplies up here urgently particularly of cooking oil and of corn-soya blend which is particularly important for feeding young children at risk of malnutrition," the WFP's Marcus Prior told BBC Radio 5 Live.
"Forty per cent of those people displaced are children and this operation is particularly urgent because people left their homes with really nothing at all."
The Red Cross are arranging transport and security to make sure the food gets where it is needed.
A group of independent UN rights experts on Friday said they were "profoundly alarmed" by reports of incitement to racial hatred and growing frictions between Kenya's different ethnic groups.
Kenyan politics has been dogged by ethnic tensions since independence in 1963.
Mr Kibaki depends for support on the largest ethnic group, the Kikuyus, while the western Luo and Kalenjin groups - who seek greater autonomy - back Mr Odinga.
KENYA'S ETHNIC GROUPS
Population 34.5m, comprising more than 40 ethnic groups
Kikuyu are the largest tribe, mostly concentrated around Nairobi
Most of Eastern/ North-eastern regions sparsely populated with ethnic Somalis
Main ethnic groups are:
Other African: 15%