A Syrian opposition activist and her journalist daughter have been found murdered in their apartment in Istanbul, the Istanbul police department said on Friday.

The bodies of 60-year-old Orouba Barakat and her US-born 23-year-old daughter Halla were found overnight in their apartment in Istanbul's Uskudar neighbourhood in the Asian side of the city.

Halla Barakat, an American citizen, had just graduated from Istanbul's prestigious Sehir University and was working for the Istanbul-based Syrian opposition-run television channel Orient News.

She was the cousin of Deah Barakat, who was one of three murder victims in what became to be known as the Chapel Hill shootings in the US state of North Carolina in February 2015.

Turkish media reports said Orouba Barakat was investigating alleged torture in prisons run by the Syrian regime.

According to people close to the family, both women had recently been threatened.

"The hand of tyranny and injustice assassinated my sister Doctor Orouba and her daughter Halla in their apartment in Istanbul," Orouba's sister Shaza wrote on Facebook, adding that they were stabbed to death.

"Orouba wrote headlines in the first page and she pursued criminals and exposed them. Her name and her daughter's name, Hala, now made first page headlines," Shaza added.

Since the outbreak of the Syrian civil war in 2011, Turkey has become home to almost three million Syrian refugees, many of them opponents of the regime of Bashar al Assad.

Source: TRT World