Emlyn Culverwell‚ 29, and Iryna Nohai, 27, were arrested in January for sex outside marriage, which is prohibited in the UAE. News of their detention surfaced earlier this week.
Culverwell's mother, from South Africa, has pleaded for the couple's release, saying "the only thing they did wrong was fall in love".
She said her son - who had been working in the UAE for five years - and his Ukrainian fiancee have not yet been charged and are still being investigated.
"It must feel as if she is being raped by the authorities," she said. "The only thing they did which was wrong, was to fall in love. It makes no sense."
The foreign ministry of South Africa said it was unable to interfere as it is a matter of domestic UAE law, according to News24.
In the UAE, sex outside marriage is unlawful although authorities usually turn a blind eye to foreign couples who live together.
If the couple are found guilty, they could face a long imprisonment.
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