Greek police say they have arrested a 49-year-old man that is believed to have been supplying weapons to Hezbollah.
The suspect, who holds American as well as Jordanian nationality, was arrested at a hotel in Aspropyrgos, west of Athens, on Tuesday.
Greek authorities are said to have acted on a tip from US intelligence.
The suspect, who arrived in Greece on a plane from Egypt on Monday, had been under surveillance. His visit has been linked to the purchase of weapons and ammunition.
The suspect, whose name was not made available, will face a prosecutor in the coming days.
Hezbollah is a Shia Muslim group and political party based in Lebanon.