Zimbabwe's ruling party declared Friday that a presidential runoff election will be held between President Robert Mugabe and opposition rival Morgan Tsvangirai, as the opposition party said it was going to court in its fight to have results from the first vote released.

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Workers remove campaign posters of President Robert Mugabe in Harare Friday. ((Tsvangirayi Mukwazhi/Associated Press) )

The announcements came as police cracked down on foreign reporters and opposition politicians in a move diplomats said could indicate Mugabe is poised to declare emergency rule after losing parliamentary elections last week.

The Zimbabwean electoral commission has yet to release results from Saturday's presidential vote, which the opposition says is "unjustified." The suit filed late Friday at the Harare High Court is to be heard Saturday.

Just hours earlier, Mugabe's Zimbabwe African National Union-Patriotic Front, or ZANU-PF, announced the runoff following a five-hour meeting with senior party officials. Party secretary and Minister of State Didymus Mutasa also charged that the opposition bribed electoral officials and said his party would contest results of 16 parliamentary seats.

Officials in Mugabe's government privately acknowledged they "have not won the absolute vast majority they thought they were going to get" and are now preparing for a runoff, said the CBC's Adrienne Arsenault, who spoke with deputy information minister Bright Matonga after the meeting.

"[Matonga's] description of it was that the last election process was a bit like a rehearsal, a bit like a warm-up. The next one will be the real match …and [he said] the government will win it," she reported from the capital, Harare.

Diplomats in Harare and at the United Nations said Friday they think Mugabe is planning to declare a 90-day delay to a presidential run-off in order to create time for security forces to clamp down on the opposition.

The opposition Movement for Democratic Change (MDC) said they believe their candidate secured enough votes to be declared the winner.

But independent observers had projected a runoff, saying Tsvangirai won the most votes, but not the 50 per cent plus one vote necessary for an outright victory.

Zimbabwean law requires a runoff be held within 21 days of an election, but Mugabe could change that with a presidential decree, an unnamed Western diplomat in Harare said.

The announcement came on the same day as a group of so-called "war veterans," a group considered as Mugabe's shock troops, marched through the streets of Harare, further unnerving residents who are fearful of what may come amid the crisis.

"They remember the fights of the past," the CBC's Arsenault said. "Some people see it as threatening."

Opposition offices ransacked, MDC says

Tsvangirai's party has been officially declared the winner of the country's parliamentary elections, held March 29. Results from the presidential election are yet to be released by the Zimbabwe Electoral Commission, although Matonga said he thought full results would be announced by the end of Friday.

Heavily armed riot police raided MDC party offices, as well as hotels used by foreign journalists, in Harare Thursday. Five reporters were detained.

MDC secretary-general Tendai Biti said hotel rooms used as offices by the opposition were ransacked by intruders he thought were either police or agents of the Central Intelligence Organization.

"Mugabe has started a crackdown," Biti said. "It is quite clear he has unleashed a war."

Biti said the raid at the Meikles Hotel in Harare targeted "certain people … including myself," but that Tsvangirai was "safe."

On Friday, a police escort accompanied about 400 veterans of Zimbabwe's guerrilla war for black rule as they marched through Harare in a show of support for Mugabe.

110 of 210 Assembly seats go to anti-Mugabe forces

The United States Friday called for a quick resolution to the uncertainty surrounding Zimbabwe's elections, saying it was "troubled" by the reports of arrests.

"We're troubled by the reports we're hearing on the ground," White House spokesman Gordon Johndroe told reporters at the NATO summit in Bucharest. "Journalists and NGOs should be permitted to go about their business."

Mugabe's party won 97 of the 210 seats in the House of Assembly while the opposition Movement for Democratic Change (MDC) won 99 seats, the state-run newspaper The Herald reported Thursday. A breakaway MDC faction won 10 seats, and an independent candidate won one. Results of three byelections aren't available.

The breakaway faction of the opposition indicated Friday it would back Tsvangirai in a runoff.

"Whatever formation is there to remove Mugabe, we are there to support it," Abednico Bhebhe, spokesman for the faction headed by Arthur Mutambara, told the Associated Press.

Mugabe, a former anti-colonial fighter, is facing the greatest challenge to his 28-year grip on power, which has been tarnished in recent years with an economic collapse that has seen annual inflation rise above 100,000 per cent and unemployment run at 80 per cent.

With files from the Associated Press