LEIDSCHENDAM, Netherlands - The UN-backed court investigating the 2005 assassination of former Lebanese Prime Minister Rafik Hariri has widened its probe to cover three other attacks they believe could be linked, the court announced Friday.

The Special Tribunal for Lebanon said it has established jurisdiction over the June 2005 assassination of anti-Syria politician George Hawi. It also will investigate unsuccessful attempts to kill Deputy Prime Minister and Defense Minister Elias Murr a month later and lawmaker Marwan Hamadeh in October 2004.

The court released few details of the decisions to widen the scope of its investigation, saying it did not want to compromise its work.

It did not release details on why prosecutors believe the three other attacks may be related to Hariri's assassination.

The expansion of the case, however, represents a significant escalation in the work of the court that has so far focussed solely on the Feb. 14, 2005, suicide bombing that killed Hariri.

The tribunal on Wednesday unsealed an indictment accusing four members of the Iranian-backed Hezbollah group of involvement in the Hariri assassination. Hezbollah denies involvement and has vowed not to hand over suspects.

Under the court's rules, it can investigate other attacks if they are of a "similar nature and gravity" to the bombing that killed Hariri and 22 others, including the suicide bomber. They must also share elements such as motive and suspected perpetrators.

Hawi, a former Communist Party leader, was killed June 21, 2005, by a bomb placed under his car. Murr survived a car bombing that targeted his vehicle as he drove on a north Beirut suburban street. Murr later said he was threatened by Syria's intelligence chief in Lebanon. Hamadeh survived a 2004 car bomb.

Prosecutors have asked Lebanese authorities to turn over their files regarding the attacks and will combine that information with their own investigations before deciding whether to issue more indictments.