Turkey says it has seized a large quantity of missiles, rocket launchers and other arms from a ship which was heading from Ukraine to Egypt.
Customs officials said the weapons were found in two containers after the ship was searched at the port of Ambarli on the north shore of the Sea of Marmara.
The ship's crew was arrested and an investigation was launched.
Turkey has boosted security ahead of this month's Nato summit in Istanbul, to be attended by world leaders.
Last month, police in the north-western city of Bursa said they had foiled a plan to attack the summit.
Nine people were charged in connection with the alleged plot.