ABU DHABI (AFP) - Saudi Oil Minister Ali al-Naimi said Sunday he was confident world prices would improve after a slide he blamed partly on "lack of cooperation" by producers outside the OPEC cartel.

"I am confident that oil markets will recover... and that oil prices will improve," Naimi told an energy forum in Abu Dhabi.

He said the sharp drop in prices was partly due to the "lack of cooperation by main producing countries outside OPEC, misleading information and speculators' greed."

Naimi, whose country is OPEC's leading producer, said producers from outside the cartel would eventually "realise the importance of cooperation to secure new fair prices". He predicted that "high-cost producers will not continue to increase production," in a clear reference to shale and sand oil output from North America.

Naimi dismissed claims of a Saudi "plot" to push prices down for political goals, insisting that the kingdom's policy is "based on pure economic principles."

"Recently, certain analyses and articles have spoken of a politically motivated Saudi plot, using oil and its prices against this country or that... This is baseless," he said.

Russia and OPEC-member Iran, whose economies rely heavily on oil revenues, have spoken of a conspiracy in the oil market to keep prices low.