UPDATE 1-Lebanon impounds ship carrying Libyan weapons
* Lebanon army says seizes arms shipment
* Pictures show weapons crates with Libyan markings
* Owner says unaware ship carried weapons (Adds comments from ship owner)
BEIRUT, April 28 (Reuters) - Lebanese authorities seized a large consignment of Libyan weapons including rocket-propelled grenades and heavy calibre ammunition from a ship intercepted in the Mediterranean, the army said on Saturday.
It did not say where the vessel was heading but the ship's owner told Reuters it was due to unload in the northern Lebanese port of Tripoli.
The mainly Sunni Muslim city has seen regular protests in support of the 13-month uprising against President Bashar al-Assad in neighbouring Syria, and any arms shipped there could have been smuggled across the border to anti-Assad rebels.
The army said in a statement the weapons were found in three containers carried by the Sierra Leone-flagged Letfallah II, which was impounded along with its 11-man crew and taken to a navy port in Beirut.
Pictures released by the army showed dozens of crates inside the containers, some of them filled with belts of heavy ammunition and rocket-propelled grenades.
Labelling on one box said it contained fragmentation explosives, and several identified them as coming from Libya.
One was marked "Tripoli/Benghazi SPLAJ", referring to LIbya's formal name during the 42-year rule of Muammar Gaddafi - the Socialist People's Libyan Arab Jamahiriya.
Another was stamped Misrata, the Libyan town which formed a base for rebels who overthrew Gaddafi last year in one of several uprising which swept the Arab world.
Russia accused Libya in March of arming and training Syrian rebels. Libya's prime minister said he was unaware of training camps in his country but repeated Libya's strong support for Syrians "who are raising their voice asking for freedom".
Syrian authorities have repeatedly said weapons are being smuggled from neighbouring countries, including Lebanon, to arm rebels fighting Assad.
Ship owner Mohammad Khafaji said he was told the craft was carrying engine oil, and was unaware of any weapons. "The law doesn't allow me to open and inspect the containers," he said by telephone from Egypt.
Khafaji said a broker from Lebanon had made contact, asking originally for a shipment of 12 containers of "general cargo" to be shipped from Libya to Lebanon. In the end, after two days' delay, the ship left with just the three containers, he said.
It sailed to Turkey and then the Egyptian port of Alexandria before heading for Tripoli in Lebanon, but as it was completing formalities for docking there the crew was told to take the ship to another port, Selaata, to unload the cargo.
"After that we lost contact with the crew," he said. (Additional reporting by Nazih Siddiq in Tripoli; Editing by Andrew Heavens)