The deadline for the investigation of the deadly terror attack in Bulgaria last summer has been extended by five months, according to Kalina Chapkanova, the Prosecutor monitoring the case.

July 18 will mark one year since the bus bombing at the Sarafovo airport of the Black Sea city of Burgas that killed six Israeli tourists, their Bulgarian bus driver, Mustafa Kiosov, and the bomber.

Chapkanova explains the investigation is at a very advanced stage. 150 witnesses have been interrogated, a large number of expert reports have been carried out, and the reenactment of the attack had additionally helped the probe.

Last week, the new leadership of the Ministry of Interior said it stood behind the "reasonable assumption," first voiced by the former Interior Minister Tsvetan Tsvetanov in the Cabinet of the Citizens for European Development of Bulgaria party, GERB that the Lebanese militant group Hezbollah is responsible for the Burgas bombing.

Announcing plans for reforms in the security sector last Thursday, Interior Minister Tsvetlin Yovchev and Chief Secretary Svetlozar Lazarov, made clear the stance of the Ministry on the terror attack.

"There is no change in the Bulgarian stance on the act of terror in Sarafovo. My expert opinion, as I am acquainted with the conclusions and the facts, gathered up to now in the investigation, is that the announced stance of my colleagues is right and I support it," the Interior Minister stated.

Yovchev added that the recent collection of "additional evidence" on the matter also leads to the conclusion that Hezbollah is responsible for the bombing.

Bulgaria's new Foreign Minister Christian Vigenin said on June 5 that "the evidence is not categorical" that Hezbollah planned the attack.

International media then commented that the Balkan country had "backed away from charges" that the Shi'ite Muslim militant group had carried out the attack.

The European Union is expected to make a decision in late 2013 whether to designate Hezbollah as a terrorist organization as the US has done years ago.