A Bulgarian journalist who reported on an investigation into alleged corruption involving European Union funds has been murdered in the Danube town of Ruse, authorities said on Sunday.

Prosecutors in the Balkan country said that the body of 30-year-old Viktoria Marinova was found in a park in Ruse on Saturday. They identified her only by her initials.

"It is about rape and murder," Interior Minister Mladen Marinov told reporters. He said there was no evidence to suggest the murder was related to Marinova's work and there was no information that she had been threatened.

Bulgarian Prime Minister Boyko Borissov told reporters: "I am convinced it is a matter of time before the murder would be revealed. The best criminologists were sent to Ruse, let's not press them. A large amount of DNA had been obtained."

Police are expected to disclose more details on Monday.

"Her death was caused by blows to the head and suffocation, and her mobile phone, car keys, glasses and some of her clothing were missing," Ruse regional prosecutor Georgy Georgiev said.

Marinova, who was a board member of the Ruse-based TV station TVN - one of the most popular TV channels in northeastern Bulgaria - is the third journalist to have been murdered in the European Union in a year.

Local media reported that Marinova had recently been involved in covering an investigation by a group of Bulgarian journalists into companies involved in EU-funded infrastructure projects administered by local authorities.

Last October, Daphne Caruana Galizia, Malta's best-known investigative journalist, was killed when a powerful bomb blew up her car and Slovak journalist Jan Kuciak was shot dead in February.

"With great pain and insurmountable grief the TVN's team is experiencing the loss of our beloved colleague Victoria Marinova and we pray for sympathy to the sorrow of her relatives and colleagues," TVN said in a short statement.

Bulgaria ranked 111 out of 180 countries in the Reporters Without Borders world press freedom index this year, lower than any other EU member and also lower than other countries in the western Balkans, some of which are candidates for EU membership.

In October 2017, hundreds of Bulgarian journalists protested in downtown Sofia downtown against threats from Deputy Prime Minister Valeri Simeonov against the country's biggest broadcasters. He accused the mainstream media of leading a "massive smear campaign" against him.

--Reuters