BUDAPEST (Reuters) - Croatian Deputy Prime Minister Radimir Cacic was sentenced to 22-months in prison by a Hungarian court on Wednesday for causing a fatal car crash in Hungary in 2010, a court spokesman and his lawyer said.

Cacic, who is also economy minister and Prime Minister Zoran Milanovic's closest ally in the centre-left cabinet, said earlier he would step down if sent to prison.

Attila Vadocz, spokesman for the Kaposvar court, told Reuters the sentence was not open to appeal.

In a previous ruling in June, Cacic was given a suspended sentence. Wednesday's ruling overturned that sentence.

"This means that the one year, 10 month prison ruling must be carried out," Vadocz said, adding Cacic could be released on parole after spending half of the 22 months in prison.

Cacic was not immediately available for comment.

Vadocz said those convicted must generally start their sentences in one or two months after the ruling.

The sentence is a major blow to Milanovic. Cacic has been tasked with kick-starting a public sector investment program in energy and infrastructure which the year-old government hopes will help economic recovery after four years without growth.

Cacic was driving on Hungary's main motorway in 2010 when he collided with another car. The impact injured two passengers, who later died in hospital.

Cacic acknowledged his guilt but said he was briefly disoriented by fog on the road. He said the other car was driving too slowly and the passengers had not fastened their seat belts.

(Reporting by Gergely Szakacs and Sandor Peto; Additional reporting by Zoran Radosavljevic in Zagreb; Editing by Janet Lawrence)