Slovakia’s prime minister, Robert Fico, has hit out at journalists questioning him about allegations that public procurement rules had been broken during the country’s EU presidency, describing them as “dirty, anti-Slovak prostitutes”.

Fico has long had poor relations with media critical of him or his government, refusing questions from certain journalists and in some cases filing lawsuits.

On Wednesday he stepped up his rhetoric, becoming angry when asked about allegations made on Sunday by Zuzana Hlávková and the anti-corruption watchdog Transparency International.

“Some of you are dirty, anti-Slovak prostitutes, and I stand by my words,” Fico told journalists. “You don’t inform, you fight with the government.”

He also said the accusations were a targeted attack to smear Slovakia’s EU presidency, which ends in December.

Hlávková was part of a team at the foreign ministry tasked with organising cultural events to mark the presidency, including a ceremony in February to unveil its logo.

At a news conference on Monday held in conjunction with Transparency International, she accused her superiors of pressuring her into sidestepping public procurement for the ceremony, and working instead with an events agency close to Fico’s leftwing Smer party.

She also alleged that a concert marking the start of the presidency in July was organised without public procurement, and that the cost of organising the event had been set higher than required.

Transparency International said on its website that “feigned public procurement” was a crime and that it had asked three watchdogs to look into the case, namely Slovakia’s public procurement bureau, its anti-monopoly bureau and its supreme audit office.

Police declined to comment.

Speaking at the same news conference as Fico, the foreign minister, Miroslav Lajčák, also rejected the accusations. “Everything was in line with the law, and the budget allocated for the presidency won’t be even fully spent,” he said.