The seven, all members of the Baath party that has ruled Lebanon's neighbour for 50 years, were detained last week, the official told AFP, speaking on condition of anonymity.
Among them was a Baath "official" from the Bekaa region of eastern Lebanon bordering Syria.
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He confessed to having kidnapped a member of the Syrian rebel group Ahrar al-Sham, and is also suspected of abducting a Syrian opposition member more than a month ago in eastern Lebanon and a sheikh he handed over to the Syrian authorities.
Lebanon currently hosts more than a million Syrians who have fled the brutal war that has ravaged their country for nearly four years.
Many opponents of President Bashar al-Assad's regime, from peaceful activists to rebels, have also found refuge in Lebanon.
The conflict has deeply divided Lebanon between supporters and opponents of the Syrian regime, which held sway over its neighbour for nearly 30 years.