By Ian McWilliam BBC correspondent in Kabul

An agreement has been signed in the Turkmen capital, Ashgabat, paving the way for construction of a gas pipeline from the Central Asian republic through Afghanistan to Pakistan.

The project has been around for some years

The building of the trans-Afghanistan pipeline has been under discussion for some years but plans have been held up by Afghanistan's unstable political situation.

This follows a summit meeting bringing together the presidents of the three countries last May when the project received formal go-ahead.

The pipeline would represent the first major foreign investment in Afghanistan in many years.

Alternate route

With improved regional security after the fall of the Taleban about a year ago, Afghanistan, Turkmenistan and Pakistan have decided to push ahead with plans for the ambitious 1,500-kilometre-long gas pipeline.

Pakistan will be the terminus for the pipeline

The leaders of the three countries have now signed a framework agreement defining the legal aspects of setting up a consortium to build and operate the pipeline.

The trans-Afghanistan pipeline would export Turkmen gas via Afghanistan to Pakistani ports, from where it could reach world markets.

India is the largest potential buyer and the Afghan President, Hamid Karzai, said Delhi was welcome to join the project.

Turkmenistan has some of the world's greatest reserves of natural gas, but still relies on tightly controlled Russian pipelines to export it.

Ashgabat has long been desperate to find an alternative export route.

Wary investors

Afghanistan would profit by receiving millions of dollars in transit fees and construction of the pipeline would provide thousands of desperately needed jobs.

It is also hoped such a project would boost regional economic ties and pave the way for further foreign investment.

The chief difficulty will be actually finding the money to build the pipeline.

The Asian Development Bank is carrying out a study for the project.

But investors will be very cautious about putting serious money into Afghanistan when the central government in Kabul still has only limited influence in the regions the pipeline would cross.