The Lebanese navy intercepted three containers of weapons destined for Syrian rebel forces on board a ship originating from Libya, a security official told AFP.
The cargo of the ship contained heavy machineguns, artillery shells, rockets, rocket launchers and other explosives, a security official said.
The 11 members of the crew were arrested pending investigation by a military judge, the official National News Agency reported.
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A second official said the Sierra Leone-flagged Lutfallah II had previously obtained a permit to enter the port of Tripoli in northern Lebanon before being intercepted by the navy on Thursday night.
News reports said the ship had called at the Egyptian port of Alexandria en route from Libya.
The vessel was towed to Selaata, a small port some 50 kilometres (30 miles) north of Beirut.
A resident told AFP that the ship left Selaata under naval escort and an AFP photographer later saw the vessel docked in Beirut.
An AFP reporter saw three army trucks leave Selaata for Beirut with the seized containers, escorted by eight jeeps and a helicopter.
Syrian authorities have repeatedly charged that weapons are being smuggled from Lebanon to rebels fighting to overthrow President Bashar al-Assad.
