The report states that Iran was also involved in the bus bombing that killed five Israelis last year.
U.S. officials reportedly have said that Bulgaria will blame Hezbollah and Iran for a terrorist attack that killed five Israelis last year in the Balkan state.
Unidentified U.S. and Middle East officials who were briefed on the findings told the Wall Street Journal that Bulgaria's government is expected to release an investigative report this week containing theses conclusions.
The report is about the July 18 bus bombing that took place in Burgas, Bulgaria, and was aimed at Israeli tourists there. A Bulgarian also was killed in the attack.
A Bulgarian finding that Hezbollah was linked to the attack could lead to its classification as a terrorist group in the European Union.
The U.S. Congress in recent weeks has called on European bodies to join the United States, Israel, Canada, Australia and New Zealand in designating Hezbollah as a terrorist group.
Bulgarian Interior Minister Tsvetan Tsvetanov is scheduled to brief senior members of the Bulgarian government on the investigation's findings on Feb. 5, a spokeswoman for the ministry said but did not comment on the content of the report, according the Wall Street Journal.
British and Dutch officials pressed last year for concerted E.U. action against Hezbollah, a major player in Lebanese politics and government, but other nations including France have resisted efforts to blacklist the group in an apparent effort to maintain good relations with Beirut.