Officials from the Zimbabwean high commission were allowed to be present during the interrogations of asylum seekers at a repatriation centre in Gauteng.
This was claimed on Wednesday by Zimbabwean clergymen.
This left the asylum seekers traumatised and prompted other inmates to call the centre "a psychological torture chamber".
Home Affairs Minister Nosiviwe Mapisa-Nqakula revealed this week that she had launched an independent commission of inquiry into deaths at the Lindela Repatriation Centre near Krugersdorp.
Seven priests visited South Africa recently under the auspices of the Zimbabwe National Pastors Conference (ZNPC) to acquaint themselves with the living conditions of Zimbabweans who had fled as economic and political refugees to South Africa.
They said they agreed with the "torture chamber" description after paying a visit to Lindela last week.
The inmates awaiting deportation were terrified they would be identified as asylum seekers on their return and be persecuted.
The ZNPC team said their visit had been prompted by many reports of abuse by Zimbabweans who had been deported to their country of birth.
They had listened to horrific stories of sexual harassment of arrested female Zimbabwean refugees by members of the South African Police Service.
The priests also came across Zimbabwean children who had fled home and had to turn to prostitution for survival.
Many deported asylum seekers had been reported missing by their families. It was not easy to prove the allegations, as Zimbabwean refugees were not in regular contact with their families while in South Africa or during deportations and could have returned to South Africa.
The priests said a group of 20 blind Zimbabweans had been rounded up and deported last week. Many blind Zimbabweans are going to places like Johannesburg to beg because the money they get on Zimbabwe's streets is worthless.
Reverend Nicholas Mukaronda said it was tragic that blind people should be treated this way, even though they were actually more economic refugees than political ones.
During the ZNPC team's tour of Lindela last week, they met a group of Zimbabweans due to be deported on the same day.
"They were tormented souls," said Brother Jonah Gokovah.
"The would-be deportees claimed they had been brutalised after having being picked up by the police and thrown into the back of a bakkie."
At Lindela, they were interviewed by officials from the Zimbabwean high commission in Pretoria.
"How can the same people who work for a government that caused these people to flee be invited to come to interview and help in assessing their stories?" asked Gokovah.
The involvement of Zimbabwean officials enabled their government to commit acts of retribution when the asylum seekers return, Gokovah asserted.
The lack of any appeal process at Lindela only worsened matters. With no money to contact lawyers to intervene and assist them, they were left to the whims of officials at the camp, he added.
"This is why we concluded that Lindela resembles a concentration camp," said Gokovah.
"The outcome was a matter of chance - you may either survive the process or fail and die on being returned to Zimbabwe."
The "no war in Zimbabwe attitude" of South African authorities had given officials the green light to abuse Zimbabweans at Lindela, he said.
Gauteng Police Commissioner Perumal Naidoo had confirmed to the priests that various complaints had been received, but also claimed they had not been detailed enough to identify the culprits.
Apart from ill treatment at Lindela, Zimbabwean refugees found they had jumped from the frying pan into the fire, according to testimonies the priests received during a week of ministry to Zimbabweans in communities around Johannesburg.
"Zimbabweans in South Africa are living in more terror and misery than they fled from," said Reverend Vimbai Mugwidi of the Methodist Church.
Apart from their harassment by police authorities and wholesale deportations, many had no shelter or food and were living in virtual squalor. Their failure to obtain refugee permits meant they could not be formally employed.
If the Methodist Church in central Johannesburg had not opened its halls to homeless Zimbabweans at night, the situation would have been even worse. She thanked those South African churches and other institutions trying to help Zimbabweans.
Mugwidi encouraged Zimbabwean exiles to file detailed complaints at police stations.
She said Naidoo had promised the team he would ensure that all people, including arrested Zimbabwean immigrants, were treated as human beings regardless of their status.