Kenya's President Mwai Kibaki has named new ministers, just before Ghana's leader arrived as part of mediation efforts following disputed elections.
Raila Odinga (r) says Mwai Kibaki (l) stole the election
No-one from the main opposition party was appointed and members of the party have said they will not recognise the new cabinet.
A BBC correspondent says the move could derail the efforts of Ghana's John Kufuor, who heads the African Union.
Violence broke out in opposition strongholds following the announcement.
Mr Kibaki gave the announcement in an address to the nation, which he recorded before going to the airport to welcome Mr Kufuor.
"In naming the cabinet, I have considered the importance of keeping the country united, peaceful and prosperous and a strong broad-based leadership," he said.
But the opposition rejected the cabinet.
"It has absolutely no legal standing, having been nominated by a president who himself is illegitimately sworn in, into office, completely in violation of our constitution," said Anyang Nyongo, secretary-general of the opposition Orange Democratic Movement (ODM).
ODM leader Raila Odinga, who claims that fraud robbed him of victory, says Mr Kibaki should step down and new polls be conducted.
In that context, the BBC's Adam Mynott in Nairobi says Mr Kibaki's move, in naming some members of his new cabinet, could be seen as a provocative act.
Some 600 people have died in a wave of clashes across Kenya after the opposition said the election had been rigged.
Residents of the western town of Kisumu say that three people have died in the latest clashes but local police chief Grace Kahindi denied this.
Kalonzo Musyoka: Vice-president, ODM- Kenya
Uhuru Kenyatta: Local government, Kanu
Moses Wetangula: Foreign affairs, PNU
Kiraitu Murungi, Energy, PNU
Martha Karua , Justice, PNU
George Saitoti: Internal Security, PNU
John Michuki : Road transport, PNU
Kisumu on Lake Victoria is Mr Odinga's home town and was the scene of serious fighting and violence last week, which left 100 people dead.
"The youth are unhappy with the announcement of the new cabinet, which they term as provocation," local reporter Joe Ojuang told the BBC News website.
There are reports that fires have been started and property looted, while police have been firing over the heads of crowds of people on the streets.
In nearby Eldoret, which witnessed the torching of a church last week, people who had returned after five days violence have started fleeing, boarding vehicles with their belongings.
The BBC's Wanyama wa Chebusiri in the town says they fear an imminent attack by opposition supporters because of Mr Kibaki's cabinet announcement and do not want to take any chances.
Armed policemen in riot gear have returned to the streets, he says.
With Mr Kibaki naming only half of the cabinet, correspondents say the implication is that other posts are being left open for the outcome of negotiations.
However, they say it is the key ministries that have been filled, leaving 15 remaining posts.
Mr Kibaki named Kalonzo Musyoka, who came third in last month's election, as vice-president.
The 17 cabinet members named include at least one other member of Mr Musyoka's party, as well as Uhuru Kenyatta, from the former ruling Kanu party.
Mr Musyoka's Orange Democratic Movement-Kenya split from Mr Odinga's party last year in a row over who should represent the party.
While many former cabinet members lost their seats in the parliamentary elections, Mr Kibaki has retained several close allies from his Party of National Unity (PNU).
They include Energy Minister Kiraitu Murungi, who has previously been sacked as a minister over a huge corruption scandal.
Mr Kufuor's trip was seen as a sign that there has been some progress on the meditation front as his visit last week had been blocked.
The BBC's West Africa correspondent Will Ross says Mr Kufuor is not someone to bash heads together - he is known as the "gentle giant" - and has helped negotiate during the conflicts in Ivory Coast and Liberia.
Both sides have accused the other of ethnic-cleansing during a week of violence after Mr Kibaki was declared the winner.
Some 250,000 people have fled their homes in clashes between rival political supporters, ethnic groups and the police.