Kenyans and world powers alike have called on President Mwai Kibaki and opposition leader Raila Odinga to agree a deal to halt turmoil that has also displaced 300,000 people.

Odinga's Orange Democratic Movement (ODM) is demanding constitutional changes creating a powerful post of prime minister for their man -- something Kibaki's Party of National Unity (PNU) has looked unlikely to concede.

As anxiety over the delays grew, the opposition accused the government of not being a "serious partner" in the talks, and of "procrastinating" to cement its hold on power.

"The ODM proposes that parliament be summoned within the next week to enact the necessary changes in the constitution to implement these mediation proposals," said an ODM statement. If that does not happen ODM will resume peaceful mass action."

Previous opposition protests after the vote brought mayhem and deaths to Kenyan cities as demonstrators battled police. The chaos has caused massive damage to the region's largest economy.

The government accused the opposition of bullying tactics.

"As mediators, we are immune to intimidation or blackmail, we will continue as though they (the threats) are not there," government negotiator Mutula Kilonzo told reporters.

But mediator and former U.N. boss Kofi Annan remained upbeat.

"Despite discouraging reports prompted by statements from one side or the other, the chair wishes to assure the public that the talks are going well and we are on track," said a statement issued on his behalf.

The opposition accuses Kibaki's team of stealing victory at the December 27 polls. Kibaki's side says it won fairly and accuses ODM of instigating tribal violence following the final results.

The government team is resisting calls by U.S. Secretary of State Condoleezza Rice, chief mediator Annan and other nations to allow a power-sharing deal or "grand coalition".

CONSTITUTION DEBATE

On Tuesday, Kibaki said he was "willing to work together and share responsibilities in government" with ODM, but that any deal "must be in tandem with the current Kenyan constitution".

The government's insistence on sticking to the constitution -- a colonial-era treaty which all sides agree is long overdue for reform -- could block any special new arrangement to accommodate ODM like a premier's post for Odinga, analysts say.

Another senior opposition official, Najib Balala, said ODM was becoming "impatient" and would consider other options given international pressure has not swayed Kibaki.

"The only thing they can listen to is the power of the people and I think that power needs to be revived," he said, also hinting at an ethnic isolation of Kibaki's Kikuyu group, whose homeland is the central highlands.

"If negotiations are not working, then we change the terms of reference of negotiations of discussing boundaries and reducing them to an island like Lesotho."

Many Kenyans fear a return to bloodshed if a final deal is not struck soon, and local media say gangs in some conflict-hit areas have been re-arming with crude weapons.