TEHRAN -- Chinese President Jiang Zemin will make an official visit to Iran at the head of a top political and economic delegation in April, the Chinese Embassy said Monday.

The exact date has not been fixed but it would be "around mid-April", an Embassy source said.

The announcement came as talks on energy cooperation were being held in Tehran at a meeting of a joint Iranian-Chinese Joint Economic Commission.

"Long term contracts for purchase of crude oil from Iran and cooperation in the strategic gas sector are highly important to China", the Head of the Chinese delegation, Wu Yi, told Iran's IRNA news agency.

This was the first time that sales of Iran's gas to China had been discussed by experts and officially announced.

China has been active in Iran in different fields, including construction of a power plant, highways, and Tehran's subway and airport, and is also building five oil tankers for the Iranian merchant fleet.

Nuclear cooperation between the two countries was stopped in late 1999 but in January Washington angered Beijing by slapping sanctions on three Chinese firms accused of supplying Iran with materials used to make chemical and biological weapons.

Chinese Vice President Hu Jintao said in Tehran in January last year that Jiang had agreed to come to Iran on an official state visit at a date to be fixed.

Iran's President Mohammad Khatami visited China in June 2000.