Roads were closed outside and riot police ringed the building in downtown Nairobi as President Mwai Kibaki and opposition leader Raila Odinga entered parliament for the opening session, without greeting each other.

It was the first time they had been present in the same room since the disputed December 27 vote.

Pro-Kibaki legislators stood up when the president came in, while opposition members of parliament stayed sitting down.

In the 222-seat parliament, the opposition Orange Democratic Movement (ODM), which says Kibaki stole the vote by electoral fraud, commands the highest number of seats, 99.

It hopes to elect its candidate Kenneth Marende as speaker.

"It's going to be very acrimonious. We should definitely expect some drama," political analyst X.N. Iraki said.

ODM, which the government also accuses of stuffing ballots and altering tallies in its strongholds during the election, also plans to block future government work in parliament.

The sitting of parliament begins a new period of high tension after a lull in the crisis, with ODM planning to stage a wave of banned street demonstrations from Wednesday.

Former U.N. head Kofi Annan was due to fly into Nairobi on Tuesday night to head a group of "Eminent Africans" trying to mediate between Kibaki and opposition leader Raila Odinga.

Joining Annan are Graca Machel, wife of Nelson Mandela, and former Tanzanian President Benjamin Mkapa.

Turmoil since the presidential and parliamentary elections has killed at least 612 people, dismayed foreign donors, jeopardised Kenya's democratic credentials and hurt one of Africa's brightest economies.

Western powers, and Kenya's east African neighbours, have complained of irregularities in the presidential vote count.

In the toughest action from the West since the crisis began, the European Union threatened late on Monday to cut aid.

"INTEGRITY AND SOBRIETY"

Kibaki's Party of National Unity (PNU) won 43 seats in the parliamentary election. But it believes it can garner enough support from other parties to control the law-making body.

Kibaki, 76, and Odinga, 63 -- a one-time member of his cabinet and former political prisoner -- were facing each for the first time since the vote as parliament was sworn in.

Media and civil society groups urged the two sides to put national unity and peace before their dispute.

"We call for integrity and sobriety in parliament ... Kenyans expect a lot," the Standard newspaper said. "Accolades should go to those who aspire to heal the nation; barbs must go the way of those whose mission will be to light more fires."

Diplomatic efforts to get Kibaki and Odinga to negotiate appeared to suffer a blow on Monday when a senior minister and close Kibaki ally rejected Annan's mission.

"He's not coming at our invitation," said Roads and Public Works Minister John Michuki. "We won an election. We don't have a problem to be solved here."

But the Foreign Ministry, in a statement on Tuesday, welcomed the Annan mission "to facilitate dialogue".

Though the presidential vote was widely perceived to be flawed, the parliamentary ballot was given a relatively clean bill of health by most independent observers.

After parliament's opening, the opposition plans three days of nationwide anti-Kibaki protests from midday on Wednesday.

Police have banned the rallies and many expatriates are leaving Kenya in anticipation of trouble. The United Nations' 4,000 staff in Nairobi were on a Phase 2 alert -- of three levels -- meaning only essential staff were at desks.

In Nairobi's Mathare slum on Tuesday, crowds shouted "No Raila, no peace!" and taunted policemen on patrol. Some shouted "kesho", tomorrow in Swahili, in reference to the rallies.

Around 250,000 Kenyans are still living as refugees from the violence -- an irony in a nation long used to receiving the homeless from neighbouring hot-spots like Somalia and Sudan.