Tendai Biti, the MDC secretary-general, told South African radio: "They [the police] were at the hotel we have been using as an information centre. They went into the rooms we have been using. I don't know what they were looking for."
But police dismissed claims.
Wayne Bvudzijena, a police spokesman, said: "What the MDC is doing is to stoke tensions. It's wrong to be making those false statements. We are not aware of any raid or arrest at opposition offices.
"Whenever we raid a place, we do it within the law and we have never denied it."
"Preparing for war"
Biti said the police search at the Meikles hotel in the capital meant Mugabe and his ruling Zimbabwe African National Union - Patriotic Front party (Zanu-PF) were "preparing for a war" with the opposition over weekend polls.
Official results have still to be released six days after the election.
The MDC says its tallies show Morgan Tsvangirai, the party's leader, won an absolute majority and should be declared president immediately.
Mugabe's Zanu-PF has indicated it is gearing up for a second round run-off to try to win the 84-year-old Mugabe a sixth consecutive term and was thought to be drawing up its battle plan in its meeting on Friday.
Earlier a Zanu-PF official said Mugabe would contest a run-off vote.
"I have no doubt the resolution [at the meeting] will be in favour of a run-off, I have no doubt about that. We cannot just hand it to Morgan [Tsvangirai] on a silver platter. We will fight for it and we will win," the Reuters news agency reported a senior party member as saying.
The delay in announcing the official results has fuelled suspicion that Mugabe is buying time to stave off defeat.
|The MDC claims it's leader, Morgan Tsvangirai,|
won the election [AFP]
A runoff should be held on April 19, three weeks after the elections, but some MDC sources allege Mugabe plans to extend that to 90 days to give him time to regroup.
Nelson Chamisa, the MDC spokesman, said: "I am not aware of such a plan, but no matter how much they may want to buy time or beat up people or employ other dirty tricks, the people of Zimbabwe have already made a choice by voting for a candidate [Tsvangirai] that will take the country forward."
Analysts believe Mugabe would try to ensure victory in the second vote by declaring a state of emergency or using powerful security forces to suppress MDC supporters.
The European Commission called again on Mugabe to respect the outcome of the presidential election.
John Clancy, the commission spokesman, said: "Of course we hope the result reflects the will of the Zimbabwean people."
In a separate incident in Harare on Thursday, two foreign journalists were arrested and later charged for operating without accreditation.