SOFIA, Sept. 29 (Xinhua) -- Bulgarian law enforcement officers at the country's Kapitan Andreevo checkpoint near the border with Turkey have seized two batches of heroin with a total weight of 712.57 kg, officials said Saturday.

The illicit drug was hidden in two Iran-registered trucks carrying gypsum plasterboard from Iran to Austria, Georgi Georgiev, head of Customs Intelligence and Investigation Directorate, said at a press conference.

The two batches were found in the trucks that arrived at the checkpoint on Thursday evening and Friday respectively, the regional prosecutor Ivan Stoyanov said.

The drivers of the vehicles, Iranian citizens, were arrested at the scene, Stoyanov said.

Authorities estimated the value of the heroin on the black market would exceed 27.4 million U.S. dollars.

Bulgaria seized 602.6 kg of heroin at its borders in 2017.