SERHETABAT, Turkmenistan -- Construction has begun on the Afghanistan stretch of an ambitious pipeline that is to carry natural gas from Turkmenistan to Afghanistan, Pakistan and India.

The 1840-kilometre (1140-mile) TAPI pipeline is to carry 33 billion cubic meters of gas a year, an important new export outlet for Turkmenistan whose economy centres on its vast natural gas reserves.

On Friday, workers at the Turkmen-Afghan border welded the first link crossing the frontier in a ceremony observed on video bridge by the presidents of Turkmenistan and Afghanistan, Pakistan's prime minister and India's foreign minister.

Afghan President Ashraf Ghani said: "We are transforming TAPI into a corridor that unites the region. This is not only an economic but also a political project."

Along with the beginning of the Afghan pipeline section, construction was also started Friday on an 800-kilometre (500-mile) 500-kilovolt power line to reach Afghanistan and Pakistan and a short railway to ferry workers and pipeline construction materials into Afghanistan.