Iran and Armenia have inaugurated a natural gas pipeline intended to reduce Yerevan's reliance on gas from Russia.
Iranian President Mahmoud Ahmadinejad and his Armenian counterpart, Robert Kocharyan, opened the pipeline's first section at a ceremony near the border.
Armenia has been building closer ties with Iran following economic sanctions imposed by Azerbaijan and Turkey over the disputed Nagorno-Karabakh region.
Until now, Russia's Gazprom has supplied most of Armenia's gas.
Under the first stage of the project, Iran will deliver some 400m cubic metres (14bn cubic feet) of gas a year through the pipeline, most of which is in Iran.
But when the 141-km (88-mile) link is completed and extends to the capital, Yerevan, the volume could rise to 2.5bn cubic metres (88bn cubic feet) a year.
An agreement to build the $200m dollar project was signed in 1992 but construction only began 12 years later.
Armenia will pay for the gas with the electricity it produces at a Soviet-era nuclear power plant.