BEIRUT, Lebanon — Hassane Laqees was a major player in the Lebanese Shiite militant group Hezbollah from its inception three decades ago to its current intervention in Syria’s civil war. Over the years, he survived several assassination attempts.

But as he parked his car just after midnight on Wednesday near an apartment south of Beirut that he sometimes used, he was shot dead at close range. It was a professional-style killing that signaled a new escalation in the attacks Hezbollah has faced after plunging into the turmoil in neighboring Syria on the side of President Bashar al-Assad.

Mr. Laqees’s death was a significant loss for Hezbollah, analysts said, and any of the group’s primary enemies — Israel, the Syrian insurgents the group is battling, or their backers, such as Saudi Arabia or Lebanese Sunni militants — could have had reason to want him dead. Mr. Laqees was variously described as running the group’s telecommunications network and working to procure strategic weapons.

Hezbollah is facing “a convergence of hostilities” from Sunni militants, particularly extremists who are increasingly dominant in the Syrian insurgency and consider Shiites apostates, and from its longtime nemesis Israel, said Kamel Wazne, a Lebanese specialist on Hezbollah.