A meeting of the world's leading oil exporters to discuss capping production has ended without agreement. After hours of talks in Qatar, the country's Energy Minister Mohammed bin Saleh al-Sada said that the oil producers needed more time.Most members of the OPEC producers' group plus other oil exporters including Russia attended the talks. They wanted a deal that would freeze output and help stem the plunge in crude prices over the past 18 months. Oil prices tumbled in Asian trading as a result, with the price of both US and London crude oil down more than 5%. Talks hit difficulties earlier on Sunday as reports emerged of tensions between Iran and Saudi Arabia. Iran did not attend the meeting. Saudi Arabia, the world's largest oil exporter appeared willing to only freeze output if all OPEC members agreed including Iran. But Iran maintained it would continue the increase in oil production it has followed since economic sanctions were lifted earlier this year. The next scheduled OPEC meeting is in June.