Bulgarian police countered a terrorist attempt involving "a plane departing from a Bulgarian airport", Interior Minister Roumen Petkov told Trud newspaper.

According to information the target was a Russian Sibir Air flight that was supposed to leave Bulgaria's Varna airport on August 30 or August 31.

Interior Ministry received earlier information about an attempt targeting an airplane that was about to take off from a Bulgarian airport, Agence France-Presse reported.

"Ammunition was confiscated from the luggage of a passenger [who] was arrested," Petkov told Trud. Investigators said the woman had at least one accomplice.

Bulgarian news agency BTA quoted Interior Ministry sources as saying that the woman was a Russian citizen.

All passengers, who were supposed to board the flight underwent scrutiny, after the ammunitions were found in the luggage of the woman, BTA reported.

The woman said she was unaware of the presence of the ammunition in her belongings. She was questioned and freed after she signed a declaration to remain in the country until the investigation was completed, BTA reported.