Johannesburg - Local police said on Wednesday 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 is accused of beating model Gabriella Engels, 20, on Sunday evening at the Johannesburg hotel where her two sons were staying.- Read more: 'Grace Mugabe assaulted me with an extension cord'Engels said she suffered deep cuts to her forehead and the back of her head, and on Monday she registered a case with the police alleging assault with intent to do grievous bodily harm."We know where the suspect is," South Africa's police spokesperson Vishnu Naidoo told AFP."We are still continuing with the investigations. No warrant of arrest has been issued," he added after some reports suggested Grace 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.Grace Mugabe allegedly arrived at the Capital 20 West Hotel with bodyguards and accused Engels of partying with her sons Robert and Chatunga, who are both in their 20s and live in Johannesburg.'Kept beating me' Pictures on social media appeared to show Engels bleeding from her head after the alleged assault at the hotel in the upmarket business district of Sandton.Engels 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 News24.Zimbabwe's president is expected to fly to South Africa later this week for a regional SADC summit which opens in Pretoria on Saturday.Grace Mugabe is 41 years younger than her 93-year-old husband and the couple has two sons and a daughter.Police Minister Mbalula told reporters 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."