* EU prohibits delivery of arms from its countries to Syria
* Russian arms exporter says not aware of such shipment
* Finnlines says informed Finnish customs about cargo (Adds statement from Finnlines)
By Terhi Kinnunen
HELSINKI, Feb 15 (Reuters) - Finnish customs officials are investigating an attempt to smuggle arms to Syria through a Helsinki port in breach of an EU ban, after intercepting a container with spare parts for tanks last month.
Customs confiscated the parts, found in a container on Finnlines' Finnsun, when the vessel docked at Vuosaari port.
The container appeared have been sent from Russia to Syria, customs said in a statement, adding that there had been no requests for permission of such a delivery.
Finnlines confirmed the cargo in question was loaded in St. Petersburg on Dec. 20 and said it had raised the alarm after finding the equipment in a regular onboard audit at the port of Antwerp, Belgium.
The company decided to deliver the container to customs officials in Finland, its previous stop.
"Finnlines immediately requested the Finnish customs to restrain the cargo," it said in a statement.
Russia is one of Syria's main arms supplier and has long been an ally of President Bashar al-Assad, sending him nearly $1 billion of weapons in 2011.
The European Union prohibits the delivery of arms from its countries to Syria, where almost 70,000 people have been killed in two years of civil war, according to the United Nations.
The captain of the ship and Finnlines staff have been questioned, the customs office said, adding that it was also asking for help from other countries.
Vyacheslav Davidenko, spokesman for Rosoboronexport, Russia's state arms exporter, said he had no information about the delivery of any tank spare parts from his company to Syria, adding that they may have been confused with other arms parts.
"Sending spare parts through Finland is not exactly logical. Besides it's hard to say immediately what kind of spare parts they may be. They may look like tank spare parts, but in reality be intended for a different system," he said by telephone.
The sale and delivery of spare parts from Russia's sprawling defence industry, are often done by individual companies without the participation of the state arms exporter, making deliveries harder to track.
The director of Rosoboronexport Anatoly Isaikin said earlier this week that its deliveries to Syria were mostly air defence systems and that none of the weapons it was delivering could be used in Syria's civil war.
Moscow has blocked three U.N. Security Council resolutions aimed at putting pressure on Assad. It says his departure must not be a precondition for any negotiated settlement. (Additional reporting by Thomas Grove; Editing by Jon Boyle)