BRATISLAVA, Slovakia — A 27-year-old Slovak journalist who had been investigating corruption has been found shot to death at his home along with his fiancée, the authorities said Monday.

The killing — which appeared to be the first targeted slaying of a journalist in Slovakia’s modern history — was immediately condemned by officials, who vowed to investigate.

The journalist, Jan Kuciak, and his fiancée, Martina Kusnirova, both 27, appear to have been killed on Thursday in the village of Velka Maca, in western Slovakia, according to the office of the general prosecutor. Their bodies were found on Sunday after Ms. Kusnirova’s mother was unable to reach her.

Ms. Kusnirova was shot in the head and Mr. Kuciak in the chest, the authorities said.

“If it turned out that the death of the investigative reporter was connected to his work, it would mean an unprecedented attack on the freedom of press and democracy in Slovakia,” Prime Minister Robert Fico said in a statement.