President Gurbanguly Berdymukhamedov ordered state companies Turkmengaz and Turkmengazneftstroi to begin building the isolated republic’s section of the pipeline, state media said.
Overall, the pipeline will stretch 1,800 kilometres (1,100 miles) and is likely to cost more than $10 billion (9.3 billion euros).
The Turkmenistan official newspaper also said the government expects the gas link, with an annual capacity of 33 billion cubic metres, to be fully operational by the end of 2018.
The Turkmenistan-Afghanistan-Pakistan-India (TAPI) project could help ease growing energy deficits in Asian giants India and Pakistan.
For Turkmenistan, which has been hit by low energy prices and is dependent on China for the vast majority of its gas sales, TAPI is a key opportunity to diversify its exports.
But uncertainty hangs over the costly project. Aside from the risks associated with a link traversing war-torn Afghanistan, the four-country consortium has yet to confirm the participation of a foreign commercial partner willing to help finance it.