Government spokesman Themba Maseko warned "the situation is dire," and criticized the failure of President Robert Mugabe's government to release results nearly two weeks after the March 29 elections.
"When elections are held and results are not released two weeks after, it is obviously of great concern," Maseko said.
South African President Thabo Mbeki was widely criticized for saying last weekend that Zimbabwe was not in crisis. At a summit, Mbeki and other regional leaders issued a weak declaration that failed to criticize Zimbabwean President Mugabe.
Mbeki, appointed last year to mediate between Zimbabwe's government and opposition, has said Mugabe will not respond to a confrontational approach.
On Thursday, Zimbabwean opposition leader Morgan Tsvangirai called on Mbeki to step aside as mediator for Zimbabwe in favor of Zambia's president, who has taken a tougher stance toward Mugabe.
President Bush criticized Zimbabwe's neighbors on Thursday for failing to intercede to stop violence and misrule in the country. Other South African countries and international organizations, including the African Union, need to join the few who have come forward, Mr. Bush said.
"More leaders in the region need to speak out, and the United Nations and the AU must play an active role in resolving the situation," Mr. Bush told reporters after a White House meeting with British Prime Minister Gordon Brown.
Earlier, Secretary of State Condoleezza Rice used more forceful language, calling the past few years of Mugabe's presidency an "abomination" and urging his African neighbors to "step up" and confront the government's campaign of arrests and intimidation since the elections.
In Zimbabwe late Thursday, residents said dozens of people were rounded up and beaten at a shopping center in Chitungwiza, a suburb of the capital Harare. Among them was the head of the Zimbabwe Union of Journalists, Matthew Takaona.
Independent tallies suggest Tsvangirai won the election, but not with enough votes to avoid a runoff. The electoral commission says it cannot yet release results because it is still verifying ballots and investigating anomalies.
The opposition says Tsvangirai won outright and accuses Mugabe of engineering a delay to secure his 28-year grip on power.
Despite concerns about mounting tensions inside Zimbabwe, Maseko said South Africa cannot intervene to prevent a shipment of weapons from being transported through its territory to its landlocked neighbor as long as administrative papers are in order.
The ship, the An Yue Jiang, was anchored just outside Durban harbor after receiving permission late Wednesday to dock.
The Beeld newspaper reported it was carrying nearly 3 million rounds of ammunitions for small arms and AK-47s, about 3,500 mortars and mortar launchers, as well as 1,500 rockets for rocket-propelled grenades. The paper said it had a copy of the ship's cargo documentation, finalized on April 1 - three days after Zimbabwe's election.
Tsvangirai said Zimbabwe does not need weapons. "We are not at war," he said at a news conference Thursday in Johannesburg. "The only war that is there is Mugabe's war against the people."
A South African government official, speaking on condition of anonymity because of the sensitivity of the issue, confirmed there were weapons on board but gave no further details. Durban port authorities and police explosives inspectors could not be reached for comment.
Defense Secretary January Masilela told South African radio that the National Conventional Arms Control Committee granted approval for the transit of the weapons.
"If the buyer is the Zimbabwean sovereign government and the seller is the Chinese sovereign government, South Africa has nothing to do with that," he told the radio. He said South Africa worked according to established international conventions but had no jurisdiction over goods in transit.
The government official who approved the transit, Sydney Mufamadi, is the same official who heads the team mediating in the Zimbabwe crisis.
The South African Revenue Service said customs officials were bound by confidentiality rules and could not give details of the content of the cargo. It said the vessel would be subject to standard inspection procedures and the cargo would not be released until it was proved that it complied with customs formalities - which can be a lengthy process.
Tsvangirai said importing arms instead of food for impoverished Zimbabweans is "disgusting. It only shows the warped nature of the priorities of this regime: that they are more preoccupied with the defense-power project than anything else."