Oil prices declined after the Organization of Petroleum Exporting Countries (Opec) decided to maintain their output level, while Iran said it is ready to double oil exports if sanctions were lifted.
US benchmark West Texas Intermediate for July delivery fell 0.83% to $58.64 (£38.39, €52.74) per barrel, while Brent crude for July fell 0.68% to $62.88 as at 1.10am ET.
In a meeting on 5 June, the 12-member oil price cartel decided to go ahead with its production target, as prices recovered from a record plunge experienced in June 2014. The countries have resolved to continue oil production at a rate of 30 million barrels per day.
Meanwhile, Iran's state-run Islamic Republic News Agency reported that the country may double its overseas oil sales within six months of international sanctions ending, even if prices decline.
Sanctions were imposed on the Middle Eastern country over its nuclear programme. Iran and world powers are expected to reach an agreement on curbing Iran's nuclear enhancement before the 30 June deadline.
Despite having the world's fourth-largest oil reserves, Iran's oil exports have fallen significantly due to the sanctions. Exports have declined to 1.3 million barrels per day from more than 2.2 million barrels in 2011.
Higher exports from Iran are expected to add to the oil glut that propelled around a 50% decline in prices in 2014.
Russia may start importing crude from Iran this week as part of an oil-for-goods agreement, Iran's oil minister Bijan Namdar Zanganeh said earlier after attending the Opec meeting in Vienna.
"We believe the market will increasingly turn its attention to the risk that Iran could add new supply to the market as the June 30 deadline approaches," Morgan Stanley analysts said in a report.
"Investors will be searching for a catalyst to provide direction for oil prices," the analysts added.