Iraq could become the world's second-largest oil exporter within two decades and double its output by 2020, a major study has found.

The International Energy Agency said Iraq can overtake Russia for exports and be responsible for nearly half of all anticipated growth in global output.

But the country's government must overcome internal disputes over oil rights with the autonomous Kurdish region in the north and increase current investment from $9bn (£5.6bn) in 2011 to $25bn a year on average for the rest of the decade, the authors warned.

The IEA's chief economist, Fatih Birol, explained: "Developments in Iraq's energy sector are critical for the country's prospects and also for the health of the global economy.