Angola has denied reports it is sending 2,500 feared paramilitary police, known as the Ninjas, to Zimbabwe as a "lie".
African leaders have been loth to criticise Mr Mugabe publicly
"It is not the custom of the Angolan government to interfere in the internal matters of other governments," Angola's embassy in Harare said in a statement.
As part of a bilateral deal signed last week Angola agreed to train Zimbabwean police, a BBC correspondent says.
Meanwhile, Amnesty International says the African Union has failed to act on human rights abuses in Zimbabwe.
"What more do we need to witness before the African Union or the UN tell the Zimbabwean government 'enough is enough'?" Amnesty's Kolawole Olaniyan wrote in a letter to the UK's Guardian newspaper.
Scores of activists have been arrested and allegedly assaulted after police broke up a banned rally in Harare on 11 March.
Four senior MDC officials were prevented from leaving the country, some to seek treatment for injuries they say were sustained in police custody.
The UK Times newspaper reported on Thursday that about 2,500 Angolan paramilitary police were to be deployed in Zimbabwe to boost the security forces of President Robert Mugabe.
The BBC's Lara Pawson in Luanda says the Ninjas, so called because they are dressed in black, are feared by most Angolans for their brutality.
Zimbabwe's Home Affairs Minister Kembo Mohadi confirmed their arrival, the Times reported, adding that the first batch of 1,000 Angolans were due in April.
But our correspondent says the Angolan ministry of interior denied reports of their Zimbabwean deployment on Wednesday.
"Not a single man is being sent," Angola's interior ministry spokesman Carmo Neto told the BBC.
Our correspondent points out that Angola long denied that they had sent any sort of support - military, financial or otherwise - to assist Ivory Coast President Laurent Gbagbo in 2003, although a UN panel later insisted that they had.
Mr Olaniyan, Amnesty's Africa programme director, hit out at the international community over its inaction on Zimbabwe.
"International condemnation has freely flowed, but little action has followed. Although the African Union has called for human rights 'to be respected' in Zimbabwe, this is far too weak a response," he said.
Earlier this week, Zambian President Levy Mwanawasa likened the current crisis in Zimbabwe to the sinking of the Titanic
Over the past week, South Africa has become more forthright in its remarks, but it has not openly criticised President Mugabe's government.
More than 80% of Zimbabweans are living in poverty, with chronic unemployment and inflation running at more than 1,700% - the highest in the world.