VIENNA (Reuters) - Austrian prosecutors said on Monday they are investigating far-right leader Herbert Kickl on suspicion of breach of trust for allegedly using public funds to take out media advertising in exchange for favourable party coverage when he was a minister.

Kickl is one of several former far-right ministers - including the Freedom Party's former leader, Heinz-Christian Strache - who prosecutors said were under investigation in a statement describing the alleged scheme that would have taken place in 2018 and 2019 when they were in a coalition government.

An unnamed "media entrepreneur" was also mentioned.

"The media entrepreneur allegedly promised then-Vice Chancellor Heinz-Christian Strache favourable coverage and image enhancement for his then-party," the Central Prosecutors' Office for Economic Crimes and Corruption (WKStA) said in a statement.

"In exchange, on the orders of the respective ministers, ministries took out advertisements at the Republic of Austria's expense in media within the media entrepreneur's sphere of influence," it said.

Stache, Kickl and the Freedom Party did not respond to requests for comment.

Kickl, who was interior minister in that coalition government, now leads the party and it has a clear lead in opinion polls with a parliamentary election due by October.

Strache, who was head of the Freedom Party when it was last in government, is no longer a member of the party. He was expelled after the coalition collapsed in scandal in 2019 over a sting video that showed him offering to fix public contracts.

An unnamed Freedom Party spokesman told Der Standard, which first reported the investigation, that advertising was taken out for the proper reasons. The party was "relaxed" about the investigation and "100% convinced" it would not be taken further, the spokesman added.

Strache told Der Standard he declined to comment.

(Reporting by Francois Murphy; Editing by Andrew Heavens)