LONDON- A Dutch court has ruled a half-billion-dollar stake in the Portuguese oil company Galp linked to Angolan ex-first daughter Isabel Dos Santos must be handed over to Angola, lawyers for the southwest African country's state oil company told Reuters on Tuesday.

Dos Santos - a business tycoon who became Africa's richest woman - ran oil giant Sonangol from 2016 until 2017, when her father's four-decade rule ended.

The acquisition of the stake was "tainted by illegality, enabling Ms. Isabel dos Santos ... to reap an extraordinary financial gain to the detriment of Sonangol and, consequently, of the State of Angola", the Netherlands international arbitration tribunal was quoted as saying by Sonangol's lawyers.

Dos Santos's representatives did not immediately respond to a Reuters request for comment.

Dos Santos denied any connection to the holding company at the centre of the case - Exem - which she says was owned by her late husband. She denies any wrongdoing and says she is the subject of a political witch-hunt by Angola's new leadership.

(Editing by Alex Richardson) ((noah.browning@thomsonreuters.com;))