Supply Tremors Shake OPEC Equilibrium

Output could bounce back to close to normal around 1.4 million bpd in nine months if order were restored, Shakmak said, but was currently trickling out at not much more than a tenth of that.

Iran also vowed a quick return to the centre stage as a leading producer, but only once international sanctions over its nuclear programme are withdrawn.

Oil Minister Bijan Zanganeh said Tehran could increase oil exports by 500,000 barrels per day immediately after any lifting of sanctions.

"Very quickly we can increase by half a million and after a couple of months we can increase it to 700,000 barrels per day," he said.

But in Geneva talks, progress on solving the nuclear impasse and allowing Iran to export more oil looked stickier. They could extended for six months if no deal is reached by a July 20 deadline agreed by all parties.

OPEC has raised its 2014 demand forecast 29.76 million bpd, comfortably inside its ceiling, but the International Energy Agency, representing the United States and leading industrialized oil consumers, sees a tighter fit of around 30 million bpd.

(Additional reporting by Peg Mackey, Georgina Prodhan and Veronica Brown, editing by William Hardy)