Iranian President Mahmoud Ahmadinejad and his Armenian counterpart on Monday formally open the first stretch in Armenia of a natural gas pipeline.
Under the first stage of the project, Iran will deliver up to 400 million cubic meters (14 billion cubic feet) of gas a year; when the pipeline is completed and extends to the capital, Yerevan, the volume could rise to 2.5 billion cubic meters (88 billion cubic feet) a year.
Rain and fog prevented a helicopter flight that was to transport Ahmadinejad, and he was expected to arrive later by road.
The project was launched in 2004 after more than a decade of negotiations.
Russia, which supplies most of Armenia's gas, had objected to the project. Armenian officials said last year they were discussing the prospect of Russia's natural-gas monopoly Gazprom purchasing the Armenian section of the pipeline from Iran, the AP said.
Landlocked Armenia has developed its relations with Iran amid economic troubles caused the closing of its borders with Turkey and Azerbaijan in the wake of the conflict over Nagorno-Karabakh, a region of Azerbaijan occupied by Armenian and ethnic Armenian Karabakhi forces.
Iran also has sought projects and influence in other parts of the former Soviet Union, mostly in Central Asia.
Last year, Ahmadinejad opened an Iranian-financed tunnel improving connections between impoverished Tajikistan's north and the capital region. Tehran has focused mostly on transport and infrastructure projects and restoring historically close cultural ties.