JOHANNESBURG (Reuters) - Zimbabwe’s first lady Grace Mugabe did not make an expected appearance at a summit of regional leaders in South Africa on Saturday, following allegations of assault against her by a 20-year-old model.

FILE PHOTO: President Robert Mugabe and his wife Grace greet supporters of his ZANU (PF) party during a rally in Harare, Zimbabwe, May 25, 2016. REUTERS/Philimon Bulawayo/File Photo

South Africa has granted Grace Mugabe diplomatic immunity, a security source told Reuters on Friday.

Police had placed border posts on “red alert” to prevent her fleeing after Gabriella Engels said she was whipped by Grace Mugabe with an electric extension cable on Sunday as she waited with two friends in a luxury Johannesburg hotel suite to meet one of Mugabe’s adult sons.

Robert Mugabe, the 93-year-old president of Zimbabwe, was seen in Pretoria on Saturday attending the South African Development Community summit, but his 52-year-old wife was not at his side or part of his delegation.

While the man who has ruled Zimbabwe since 1980 was being welcomed with other heads of state in a conference hall, protesters outside the building demanded his wife face justice.

South African television reported that Grace Mugabe had not attended the summit where she had been scheduled to take part in a session for leaders’ spouses from 1000 GMT.

Harare has made no official comment on the saga and requests for comment from Zimbabwean government officials have gone unanswered. The South African government has restricted all official comment to the police ministry.

Adding to the diplomatic wrangle, South African Airways (SAA) suspended flights to Harare after one of it planes was grounded in Zimbabwe on Saturday for failing to produce an operating permit, the airline spokesman said.

“We’ve been operating for more than 20 years in that market, without this being a requirement,” said SAA spokesman Tlali Tlali, adding the airline had canceled one Harare-bound flight so far while its plane was grounded in Zimbabwe.

The move followed the grounding of an Air Zimbabwe flight in Johannesburg on Friday for not having a foreign operator’s permit on board after a random check by South Africa’s Civil Aviation Authority.