Iran has discovered seven new oil fields with 'considerable' reserves, the head of the National Iranian Oil Company has announced.

"Explorations in these oil fields in the past three years have shown that they have very high oil reserves," Seyfollah Jashnsaz told reporters on Tuesday.

He declined from giving further detail but said Oil Minister Gholam-Hossein Nozari would disclose more information about the new oil fields next month.

"All I can say for now is that one of these fields has an oil reserve of nine billion barrels which is very considerable," Jashnsaz said.

Nozari announced in March that the country's oil reserves have increased from 90 billion barrels to 138 billion barrels over the past year.

Iran, OPEC's second largest oil producer, plans to open some of its oil and gas fields to foreign investment and help boost output by 2015 to 5.3 million barrels per day (bpd), from the current 4.2 million bpd.

AKM/HGH