Iran's oil output may not rise significantly for up to five years after Tehran and world powers seal a final nuclear deal, according to the International Energy Agency (IEA).

There may not be a big growth in Iranian oil production right away as the Opec member's huge and complex fields have not been maintained "in the best way" owing to the sanctions, according to Fatih Birol, chief economist and the future head of the IEA.

But the lifting of sanctions on Iran will have a limited impact on global oil prices, Birol told Reuters on 12 April.

While lower oil prices are expected to siphon out $100bn (£68.5bn, €94bn) of investment in oil exploration and production in 2015, geopolitical tensions in the Middle East have raised questions over the security of investments by global oil firms in the region, Birol added

"In three to five years we may see stronger [oil production] growth coming from Iran assuming Iran and global powers strike a final deal in June," Birol, who will head the IEA from September, said in an interview in New Delhi.

Production and prices

Global oil firms have slashed investments by 20% in 2015, over 2014, and the IEA sees a big chunk of that investment drop in the US, Canada and Brazil.

"We have never seen such a big cut even at the time of financial crisis," Briol said, referring to the 20% cut.

"If the slowing down of production and strong growth of demand come together, this may well put upward pressure on oil [prices] in the future.

"...production growth in the US may well slow down and this is of course an important input for oil markets in next quarters to come ... It is difficult to give a number but there may be a slowdown which may have an effect on oil coming from the US in 2016," he added.

The IEA accounts for about 50% of global oil demand now, after new consumption centres such as India and China surfaced.

Oil prices have halved since June 2014 in the wake of a supply glut driven by the US shale oil boom.

Western sanctions have slashed Iran's oil exports by more than half, to around 1.1 million barrels per day (bpd) from a pre-2012 level of 2.5 million bpd. Lower oil income makes it difficult to maintain equipment and invest in new development.

OPEC