Syrian forces killed one Lebanese fisherman and wounded another when they seized their boat off the Lebanese-Syrian coast on Saturday, a relative said.
The area is known for smuggling and Syrian security services have become especially sensitive to contraband runs since a revolt against President Bashar al-Assad erupted 10 months ago.
Residents in Lebanon's northern coastal town of Arida said they heard gunfire and later saw a Syrian boat pulling the Lebanese fishing boat toward the nearby Syrian port of Tartous.
Lebanese security sources confirmed the seizure of the boat, which had three fishermen on board, but declined to give details of any casualties.
Ahmed Hamad told Reuters his wife had crossed into Syria and had found their 16-year-old son Maher Hamad dead in a Syrian state hospital. He said a second fisherman had been wounded and the third was being interrogated by Syrian security forces.
Syria complains that its neighbors are not clamping down on smuggling of weapons they say are destined for insurgents.
Dozens of angry residents and relatives of the fishermen tried to block the Arida border crossing, where they attacked a Syrian truck, smashing its windows. Security forces prevented them from entering Syria, witnesses said.