Masked gunmen roamed the streets of the border town of Arsal as Lebanese helicopter gunships flew over the town, some 88 kilometers (54 miles) from the capital, Beirut.
The army general told The Associated Press that the gunmen attacked army positions near Arsal and troops returned fire. Another official said the gunmen also took control of the main police station in the town, without elaborating.
Lebanon's state-run National News Agency reported that Arsal residents later freed police officers at the station, though rebels captured some weapons and released several detainees. It said gunmen killed two residents near the police station.
The National News Agency said that gunmen killed two soldiers and wounded several others.
The general said gunmen took a number soldiers and police officers from their homes in Arsal, as well as two soldiers who were driving an army tanker truck. It was not clear if they were taken across the border into Syria or if they were still in Arsal.
The general said the government sent reinforcements to the area. The general and the official spoke on condition of anonymity as they weren't authorized to speak publicly.
Saturday's attacks came hours after the army said troops detained Syrian citizen Imad Ahmad Jomaa, who identified himself as a member of Syria's al-Qaida-linked Nusra Front. The National News Agency said Jomaa was detained as he was being brought to a hospital in Lebanon after being wounded while fighting Syrian troops.
Syria's civil war has spilled over into Lebanon on multiple occasions and inflamed sectarian tensions leaving scores dead. However, previous rebel attacks never went so deeply into Lebanese territory.
Arsal is home to tens of thousands of Syrian refugees and rebels enjoy wide support among its population. Lebanese Sunnis, such as the residents of Arsal, often back the Sunni rebels fighting against Syrian President Bashar Assad. Shiites typically back Assad.
The violence in Arsal also came after an ambush near Syria's border with Lebanon killed dozens of opposition fighters, activists said. The Britain-based Syrian Observatory for Human rights said Syrian troops and members of Lebanon's Hezbollah group ambushed opposition fighters in the Qalamoun region near the Lebanese border, killing at least 50 of them. It said seven troops and Hezbollah fighters were killed in the fighting.
Syrian state television reported clashes in Qalamoun that killed "tens of terrorists." Syrian media refers to all opposition fighters as terrorists.
Government troops backed by Hezbollah fighters have seized nearly all the strategic Qalamoun region since launching an offensive there last November, severing rebel supply lines from neighboring Lebanon.
The Syrian uprising began in the form of peaceful protests against President Bashar Assad in March 2011, but escalated into an insurgency when government forces violently cracked down on dissent.
The country is now in the grip of a complex civil war pitting several rebel and Islamic extremist groups against the government and each other. Over 170,000 people have been killed in Syria in more than three years of fighting, activists say.