Tunisia says it has completed the first part of a 200km (125-mile) barrier along its border with Libya, designed to deter terrorism.
The barrier is made of sand banks and water trenches.
It was announced last summer after 38 people were killed on a beach by a gunman said to have trained in Libya.
Tunisia's defence minister said the second phase of the project would involve installing electronic equipment with the help of Germany and the US.
Security forces said the defences - which aim to make the border impassable by vehicles - had already helped to reduce smuggling.
"Today we finished closing it off, and this will help us protect our border, and stop the threat," said Defence Minister Farhat Horchani on Saturday.
More than 3,000 Tunisians have left to fight with the Islamic State (IS) group and other Islamist militants in Syria and Iraq but Mr Horchani said many had since returned to join the group in Libya.
Libya has been beset by instability since the overthrow of former leader Muammar Gaddafi in 2011 and currently has two rival governments.
IS took control of Sirte, Gaddafi's hometown, last year.