The Lebanese army intercepted three containers of weapons on board of a ship intercepted in the Mediterranean which may have been trying to supply Syrian rebels, security sources said on Saturday.
An overnight search uncovered weapons including rocket-propelled grenades and rifles in three freight containers, the sources said.
The Sierra Leone-flagged Lutfallah II had been given permission to dock in the port of Tripoli, an security official said.
It had made a short stopover in the Egyptian port of Alexandria en route from Libya, the official added.
It was stopped and searched in the port of Selaata, 50 kilometres (30 miles) north of Beirut, and its captain and crew were handed over to military intelligence officers in Tripoli for further questioning.
Syrian authorities have repeatedly claimed weapons are being smuggled from neighboring countries, including Lebanon, to arm rebels fighting President Bashar al-Assad.
Popular uprising asking to end the Assad regime in Syria started in March, 2011.
The United Nations says more than 9,000 people have died since the revolt erupted, while non-government groups put the figure at more than 11,100, according to Alarabiya.