The 29-year-old was a free agent after leaving Notts County in January, having made 11 appearances in all competitions this season.
"I'm happy to be at a great club," he said. "I had other offers, but I really wanted to be here."
The Ghana-born player represented Belgium at youth level and has also played for Ferencvaros in Hungary.
Meanwhile, Portsmouth first-team coach Ian Foster has left the club by mutual consent to take up a post with the Football Association at St George's Park.
Foster joined Portsmouth in May 2015 alongside manager Paul Cook and assistant Leam Richardson having previously held a similar role at Coventry City.
Find all the latest football transfers on our dedicated page.
Portsmouth have signed former Ajax and Notts County midfielder Stanley Aborah on a deal until the end of the season.