India had been part of the $7 billion so-called "peace pipeline" project, but stayed away from talks in September saying it wanted to agree transit costs through Pakistan on a bilateral basis first.
On Sunday, Iranian media said Iran and Pakistan signed their agreement during a visit by Pakistani President Asif Ali Zardari to Tehran, without giving details on its content or making clear whether there were still issues outstanding.
The head of the National Iranian Gas Export Company (NIGEC), Reza Kasaeizadeh, said Iran would deliver an annual 8 billion cubic meters of natural gas to Pakistan under the agreement.
"The matter of increasing the level of gas exports could be raised for consideration in the future upon the two parties' consent," he told the ISNA news agency on Monday.
Iran has the world's second-largest gas reserves after Russia. But sanctions, politics and construction delays have slowed its gas development, and analysts say Iran is unlikely to become a major exporter for a decade.
"FINAL AGREEMENT"
Kasaeizadeh said pricing and other issues had been finalised during two days of talks between Iranian and Pakistani officials in Tehran.
But while he said a "final agreement" would be signed during the next three weeks, Foreign Ministry spokesman Hassan Qashqavi suggested this was what happened on Sunday.
"We have reached final agreement on export of gas to Pakistan. The contract is signed," Qashqavi told a news conference in comments translated by English-language Press TV.
Asked about India, he said: "The way is not closed for the entry of the third party … India can also join this any moment it wishes to … there are no obstacles in the way."
Iran and Pakistan had agreed on a revised price formula and a new price review mechanism in December which updated terms reached in 2006 during long-running negotiations on the project.
Iran offers uniform prices to all gas clients, Kasaeizadeh said. "The base price on gas export to Pakistan would be equivalent to that of gas export to Turkey. And any price difference would pertain to distance and related costs."
The construction of the Pakistani part of the pipeline would take three-four years, he said, adding Iran was ready to help.
An Iranian Oil Ministry official had previously said he hoped the commencement of gas delivery would start five years after the contract was signed.
Under the original plans, the pipeline would initially carry 60 million cubic metres of gas daily to Pakistan and India, half for each country. The pipeline's capacity would later rise to 150 million cu metres. (Reporting by Hashem Kalantari and Fredrik Dahl; Editing by James Jukwey)
