Mr Miliband said Zimbabwe had made a "clear choice" in the election
Foreign Secretary David Miliband has said the UK "stands with" the people of Zimbabwe as it awaits the results of its recent elections.
He told MPs the country had the "opportunity" of a "democratic future".
Zimbabwe's governing Zanu-PF party has taken 94 of 210 parliamentary seats, while opposition parties have won 105.
Mr Miliband said the delayed publication of results in the presidential election was a "calculated tactic" by Robert Mugabe's regime.
Earlier, the opposition party MDC said its leader Morgan Tsvangirai had won the presidential election. Zanu-PF said this was "wishful thinking".
'Duty to announce'
Mr Miliband said that the "playing field" had been "tilted heavily" in favour of Zanu-PF and conditions for free and fair elections must be in place if a second round of voting is called.
He told MPs: "Last Saturday the people of Zimbabwe made their choice.
"Outside the 9,400 polling stations, the tallies have been posted. The Zimbabwean Electoral Commission knows what those results are, and has a duty to announce them.
"The delay in announcing the outcome can only be seen as a deliberate and calculated tactic.
"It gives substance to the suspicion that the authorities are reluctant to accept the will of the people."
Mr Miliband returned to the subject later on Wednesday, in a speech at the Lord Mayor's Easter banquet, at Mansion House in London.
"The people of Zimbabwe have spoken in their election on Saturday. Their voices must now be heard," he said.
"Many of us here will yearn for an end to the long night of suffering in that country."
Shadow foreign secretary William Hague said years of "brutality and repression" in Zimbabwe had turned it into a "political pressure-cooker".
It would take more than Mr Mugabe's departure for the country to recover from years of corruption and economic decline, he said.
Mr Hague told the BBC: "I think there's a key role here for South Africa to really show a leadership role in the region.
"They are the country that have the most leverage over Zimbabwe, and I hope they will be doing everything possible behind the scenes to make sure that the presidential results are now declared."
Ed Davey, the Lib Dems foreign affairs spokesman, urged Mr Miliband to tighten and strengthen sanctions on Zimbabwe if the Mugabe regime attempted to "cling on to power in the case of a confirmed democratic verdict".
He also said help should be given to Zimbabwe's neighbours who had sheltered millions of refugees and exiles.
Former Cabinet minister Peter Hain, who rose to prominence as an anti-apartheid campaigner, said it was "clear" Mr Mugabe had lost the election.
Earlier, Commons leader Harriet Harman, standing in for Gordon Brown at prime minister's questions, said MPs felt "concern and solidarity for the people of Zimbabwe and that they should have their democratic election respected and recognised".
Ms Harman added that the UK was Zimbabwe's biggest donor and would be "ready to step up that support" together with the international community.
Mr Brown is attending a Nato summit in Romania.