The court hearing the case of a Mitcham man accused of murdering his niece have heard he made death threats against the dead girl's sister for being too "Westernised".

Mahmod Mahmod, 52, and Ari Mahmod, 50, of Mitcham, deny charges of murdering Mahmod Mahmod's daughter Banaz, 20, whose body was found in a suitcase buried in a garden in Birmingham last April.

Banaz's sister Bekhal Mahmod, 22, told the Old Bailey jurors that she was beaten and called a whore and accused of being too Westernised.

Bekhal said she had been threatened by her uncle, Ari, after she and her cousin had been seen with a man, though she said he was just a friend.

Then a schoolgirl, she was sitting in her bedroom with her parents and her uncles, she told the court.

Ari, she said, sat on a chair cross-legged and touched the bottom of his foot to emphasise the importance of what he was saying.

"He said, 'If I was your father you would have been turned to ashes by now'," she said.

"'Your father's your father. I would have killed you by now, got rid of you'... I started crying."

Ari and Darbaz Maref-Rasull, 24, of Hounslow, west London, also deny conspiracy to pervert justice.

The trial continues.