The UN Security Council is divided over Zimbabwe, following its first discussion of the post-election crisis.
Senior opposition figure Tendai Biti had travelled to New York to lobby the Security Council members to send aid and a special envoy to Zimbabwe.
This was backed by the US and UK but opposed by countries including China and South Africa, the council’s chair.
Meanwhile, Human Rights Watch has accused Zimbabwe’s army of leading the crackdown on opposition supporters.
More than a month after the 29 March elections, the presidential results have not been released.
Mbeki has fully and squarely placed himself against the people of Zimbabwe
Tendai Biti, MDC
Movement for Democratic Change (MDC) leader Morgan Tsvangirai says he defeated President Robert Mugabe.
But independent observers and Mr Mugabe’s allies say a run-off may be needed as no candidate gained more than 50% of the vote.
The MDC says its supporters are being attacked ahead of the run-off but the ruling party says the scale of the violence is being exaggerated, while blaming it on MDC activists.
A BBC contributor in the southern town of Masvingo reports that the bodies of two opposition activists have been found after they were abducted.
In New York, UN Under-Secretary for Political Affairs Lynn Pascoe told the Security Council that Zimbabwe was in the midst of its worst humanitarian crisis since independence.
He expressed concern about a very high level of political intimidation and violence, and the “use of food as a political weapon”.
But council members could not agree on whether to take any action.
US deputy ambassador Alejandro Wolff said they could not agree on sending extra humanitarian assistance, as requested by the MDC, reports the AP news agency.
South Africa currently heads the Security Council and is also the lead negotiator between Zimbabwe’s ruling Zanu-PF and the MDC.
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George W Bush says Zimbabwe’s leader has ‘failed the country’
The MDC wants South African President Thabo Mbeki to be replaced in that role.
“Mbeki has fully and squarely placed himself against the people of Zimbabwe,” Mr Biti told the BBC’s Network Africa programme.
South Africa’s UN Ambassador Dumisani Kumalo said: “The only thing that the members seemed to agree with is that [Southern African Development Community] SADC should work with the Zimbabweans, especially their independent Electoral Commission, to make sure the results are coming out.”
In other developments:
â€¢ Foreign ministers in the European Union, which has a ban on the sale of arms to Zimbabwe, have called on other countries to impose a similar policy.
â€¢ A teachers’ union reports that teachers are fleeing rural areas after being accused of helping the opposition when they worked as election officials.
â€¢ US President George Bush has accused Mr Mugabe of “failing” and now “intimidating” the people of Zimbabwe.
â€¢ Earlier, Zimbabwe’s ambassador to the UN told the BBC that whoever won the presidential race would have to form a government of national unity.
â€¢ The final five results from a partial parliamentary recount are expected.
â€¢ State radio reports that the verification of presidential votes will start on Thursday and could take several days to complete.
â€¢ Some 180 opposition activists arrested last Friday were freed without charge.
Masvingo police chief Mhekia Tanyanyiwa has confirmed the deaths of the two MDC supporters, our contributor says.
Police sources say Zvidzai Mapurisa was abducted from his home on Saturday and beaten, before his body was found floating in a dam.
Cathrine Mukwenje was attacked by suspected ruling party militants, who gouged out one of her eyes.
She later died from her injuries.
Human Rights Watch said Zimbabwe’s army was given weapons and transport to ruling party supporters and self-styled “war veterans” who are leading such assaults.
“According to scores of victims and eyewitnesses interviewed by Human Rights Watch, Zanu-PF supporters and “war veterans” are drawing up lists of MDC activists who are then systematically targeted for abuse,” the group said.
Kucaca Phulu, chairman of the Zimbabwe Human Rights Association (Zimrights), said such assaults were “a form of rigging”.
He said hundreds of people had been forced from their homes.
The MDC says this has often been in rural areas which Zanu-PF lost in the parliamentary elections.
But Zimbabwe’s ambassador to the UN, Boniface Chidyausiku, dismissed as “totally false” the argument that the delay was to give Zanu-PF time to rig the outcome.
He pointed out that similar claims were made when the electoral commission said it was recounting 23 parliamentary results.
Eighteen of these results were announced at the weekend and were unchanged from those originally announced, meaning the opposition has a majority in parliament for the first time in Zimbabwe’s history.
But following the reports of revenge attacks by opposition supporters, Mr Mugabe’s spokesman George Charamba said the security services would use any force needed to “discourage acts that could lead to anarchy”.
Mr Biti and Mr Chidyausiku both said that a government of national unity should be formed to end the impasse.
But Zanu-PF spokesman Bright Matonga dismissed this suggestion.