South Africa police decline to say if Zimbabwe's first lady fled the country

Grace Mugabe, the wife of president Robert Mugabe, is accused of beating a 20-year-old model Gabriella Engels

File photo of Zimbabwe president Robert Mugabe and his wife Grace, who has been accused of allegedly assaulting a model in South Africa on August 13, 2017. Philimon Bulawayo/Reuters

South African police on Wednesday said they knew the whereabouts of Zimbabwe's first lady Grace Mugabe, who faces accusations of assault, but declined to say if she had fled the country.

The 52-year-old wife of president Robert Mugabe was accused of beating model Gabriella Engels, 20, on Sunday evening at the Johannesburg hotel where her two sons were staying.

Zimbabwe government sources confirmed on Tuesday that Mrs Mugabe had returned home.

"Yes, she is back in the country. We don't know where this issue of assault charges is coming from," said a senior government official, who declined to be named.

A second official also confirmed that Grace had returned, saying "she is around now" and accused the media of a plot to tarnish the first family's name.

Ms Engels said she suffered deep cuts to her forehead and the back of her head, and registered a case with the police on Monday alleging assault with intent to do grievous bodily harm.

"We know where the suspect is," South Africa's police spokesman Vishnu Naidoo said of Mrs Mugabe.

"We are still continuing with the investigations. No warrant of arrest has been issued," he added after some reports suggested Mrs Mugabe had hurriedly returned to Harare late on Tuesday.

The alleged attack threatened to spark a diplomatic tiff between the two neighbouring countries, which have strong political and economic ties.

Mrs Mugabe allegedly arrived at the Capital 20 West Hotel with bodyguards and accused Ms Engels of partying with her sons Robert and Chatunga, who are both in their 20s and live in Johannesburg.

Pictures on social media appeared to show Ms Engels bleeding from her head after the alleged assault at the hotel in the upmarket business district of Sandton.

The model said she had been attacked with an electrical extension cord.

"She flipped and just kept beating me with the plug. Over and over. I had no idea what was going on. I was surprised ... I needed to crawl out of the room before I could run away," she told the News 24 website.

Zimbabwe's president is expected to fly to South Africa later this week for a regional summit which opens in Pretoria on Saturday.

Mrs Mugabe is 41 years younger than her 93-year-old husband and the couple has two sons and a daughter.

She regularly speaks at rallies in Zimbabwe and is seen as a possible contender to take over from her increasingly frail husband.

Last month, she urged him to name his chosen successor, reviving speculation about the race to take over from the world's oldest national leader.

President Mugabe has ruled Zimbabwe since independence from British colonial rule in 1980.

South African police minister Mbalula said on Tuesday that "in terms of foreign citizens, they must understand they have responsibilities, especially those who hold diplomatic passports.

"We have had to act in the interests of the victim."