South Africa has defied a United Nations call to halt deportation of Zimbabweans and has sent 17 000 people back to the troubled country in 40 days.

This has raised fears that Zimbabweans fleeing political violence are being returned to face persecution and are unable to use South Africa's internationally guaranteed asylum-seeking processes.

Zimbabwe's opposition MDC party reported on Friday that at least 113 of its members had been killed in political violence since the country held its first round of presidential voting in March.

"Given the situation in Zimbabwe now, no one can deny that people are at risk," said Dr Loren Landau, director of Forced Migration Studies at Wits University.

The number of Zimbabweans seeking asylum had doubled to more than last year's total figure in the first quarter of this year, he said.

However, since 2000, the South African government has granted full refugee status to only 710 Zimbabweans.

Over the same period, a total of 66 578 Zimbabweans applied for asylum with 4 040 rejections in the same period. Over 62 000 cases remain pending.

On Friday, the UN High Commissioner for Refugees (UNHCR) said South Africa had sent 17 000 Zimbabweans through the Beit Bridge border post in the past 40 days.

This was despite earlier calls to suspend all deportations, said regional spokesperson Yusuf Hassan.

This also follows an assurance from Home Affairs Minister Nosiviwe Mapisa-Nqakula early last month that illegal immigrants would be "temporarily exempted" from deportation until the dust had settled on the recent xenophobic violence in South Africa.

At the time Mapisa-Nqakula announced that any foreigners illegally in South Africa would have two months to leave.

The UNHCR on Friday reiterated appeals to South Africa to exceptionally grant Zimbabweans temporary legal status and to ensure those seeking asylum have access to procedures.

The numbers of Zimbabweans fleeing to South Africa increased after that country's March general and presidential elections.

This worsened after a subsequent crackdown on opposition supporters and last month's one-man presidential run-off.

Hassan said 3 000 to 4 000 Zimbabweans were flocking to the Refugee Reception Office in Johannesburg each Thursday and Friday - asylum applications are processed regionally.

The UN had also strengthened its presence at the border and is making daily visits to the Musina detention centre to identify Zimbabwean asylum seekers and refer them to correct authorities.

"There are so many people who are deported on a daily basis, we are simply unable to interview 95% of them," said Camilla Kragelund, head of the UNHCR office in Musina. "The only Zimbabweans who are getting asylum are those who come into contact with UNHCR or our partners."

Aid workers in the border town have also reported that entire Zimbabwean families are now fleeing political violence. Previously, 90 percent of migrants were young, single men seeking better economic prospects.

South Africa is signatory to domestic and international legal obligations to not return people to danger or possible persecution.

Zimbabweans were also among the tens of thousands of foreigners affected two months ago in attacks that left more than 60 people dead.

Camps in Gauteng housing thousands of people are due to be dismantled by next month.

Thousands of people are also being accommodated in Cape Town where a meal at one shelter was sent for testing this week after it appeared rotten.

Additional reporting by Helen Bamford, Sapa-AP-AFP