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

Key points: The body of Viktoria Marinova, 30, was found in a park in Ruse, Bulgaria on Saturday

The body of Viktoria Marinova, 30, was found in a park in Ruse, Bulgaria on Saturday Bulgarian PM Boyko Borissov told reporters 'a large amount of DNA' was left at the scene

Bulgarian PM Boyko Borissov told reporters 'a large amount of DNA' was left at the scene Authorities said there was no evidence the killing was related to her work

Prosecutors in the Balkan country said 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 killing was related to Marinova's work and there was no information that she had been threatened.

Bulgarian Prime Minister Boyko Borissov told reporters a large amount of evidence had been collected at the scene.

"I am convinced it is a matter of time before the murder would be revealed," he said.

"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 north-eastern Bulgaria — is the third journalist to have been killed in the European Union in a year.

Viktoria Marinova is the third journalist to be killed in the EU in the past year. ( Facebook: Viktoria Marinova )

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.

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 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