Unions have been highly critical of Mbeki for not taking a tougher line against Zimbabwean President Robert Mugabe, who is locked in an election stalemate with the opposition over the delay of results from a March 29 election that has raised fears of violence.

The 300,000-strong South African Transport and Allied Workers Union (SATAWU) said it would not unload the weapons in the port city of Durban because Mugabe's government might use them to crack down on opponents in the disputed election.

The weapons were to be transported to land-locked Zimbabwe.

"We are concerned that the current standoff could mean the arms would fall into the hands of those who want to use military force against the people of Zimbabwe," SATAWU General Secretary Randall Howard told Reuters on Friday.

"The South African government cannot be seen as propping up a military regime," he said.

Howard said the union refused to handle four containers on the vessel which contain arms and ammunition.

A South African government spokesman has confirmed there are weapons on the ship, but said his country would not interfere in a trade matter between China and Zimbabwe.

Zimbabwe's deputy information minister, Bright Matonga, said on Friday that no party had the right to stop the shipment.

"Every country has got a right to acquire arms. There is nothing wrong with that. If they are for Zimbabwe, they will definitely come to Zimbabwe," he told South Africa's SAfm radio.

"How they are used, when they are going to be used is none of anybody's business."

The vessel, An Yue Jiang, has been cleared to dock and unload its cargo in Durban, transport officials said.

SPOTLIGHT ON CHINA

China is under an international spotlight over its human rights record and rule in Tibet ahead of hosting the Olympics in August. Violent protests have followed the Olympic torch across the globe.

China's foreign ministry said in a short faxed statement to Reuters that it had seen the reports about the ship, but "did not understand the actual situation".

"China and Zimbabwe maintain normal trade relations. What we want to stress is, China has always had a prudent and responsible attitude towards arms sales, and one of the most important principles is not to interfere in the internal affairs of other countries," said the statement.

Mugabe is under heavy international pressure to release the result of the presidential election, which the opposition Movement for Democratic Change (MDC) says it won, ending the veteran leader's long rule.

Mugabe's ZANU-PF party lost control of parliament for the first time in a parallel election, but no results have been issued yet for the presidential poll.

Mbeki, who has been acting as a regional mediator between Mugabe and the opposition, has come under fire for his quiet diplomacy in Zimbabwe. MDC leader Morgan Tsvangirai on Thursday called for Mbeki to be removed as a mediator.

"We are concerned that the Zimbabwean government will violate human rights and use these weapons against opponents," said Patrick Craven, spokesman for the COSATU umbrella trade union federation.

Mbeki's rival, ANC leader Jacob Zuma, has taken a harder line on Zimbabwe and analysts say he is capitalising on the South African president's unsuccessful mediation to boost his own image. He has wide backing from unions.

In a policy shift, Mbeki's government this week called for the results to be issued rapidly and said it was concerned by the delay.