Saudi Oil Minister Ali Al-Naimi said on Sunday that it would take "some time" to restore stability to the global oil market but he remained optimistic about the future.

Al-Naimi's comments came even as Iran said it was ready to increase its crude oil exports by 500,000 barrels a day, hours after international sanctions on Tehran were lifted, removing an obstacle to exports.

"As you know, the oil market has witnessed over its long history, periods of instability, severe price fluctuations, and petro-economic cycles," Al-Naimi said in a speech at an energy event in Riyadh attended by the Mexican president and energy minister.

"This is one of them. Market forces, as well as the cooperation among the producing nations, always lead to the restoration of stability. This, however, takes some time," he said.

"I am optimistic about the future, the return of stability to the global oil markets, the improvement of prices and the cooperation among the major producing countries," Al-Naimi added.

Brent plunged to $28.94 a barrel on Friday, for the first time in 12 years, on prospect of additional Iranian barrels.

Iran emerged from years of economic isolation on Saturday when world powers lifted sanctions after confirming that Tehran had curbed its nuclear programme.

"With consideration to global market conditions and the surplus that exists, Iran is ready to raise its crude oil exports by 500,000 barrels a day," Irran's Deputy Oil Minister Amir Hossein Zamaninia was quoted as saying by the Shana news agency.

Iran's return to an already glutted oil market is one of the factors contributing to a global rout in oil prices, which fell below $30 a barrel this week for the first time in 12 years.  - Reuters