Iran and Venezuela have reportedly reached a major oil swap deal that will see the Latin American nation exchange its heavy oil for Iranian condensate, which it can use to improve the quality of its tar-like crude.

The deal between two of Washington’s main rivals will reportedly last for six months, with an option to be extended for longer if it proves to be successful.

Neither Iranian nor Venezuelan officials have commented on the deal.

According to reports, Caracas shipped 1.9 million barrels of its Merey heavy crude to Iran after a cargo of 2 million barrels of Iranian condensate arrived in Venezuela on 23 September.

Venezuela can use the condensate to improve the quality of its oil for exports and to supply the lighter oil to refineries which can produce much-needed motor fuel.

US officials have expressed ‘concerns’ over the deal between the two sovereign nations, with a Treasury Department spokesperson saying Washington will continue to enforce sanctions on Iran and Venezuela.

According to the statement by the US Treasury Department, “any transactions with [the NIOC, the National Iranian Oil Company] by non-US persons are generally subject to secondary sanctions.” The department also said it “retains authority to impose sanctions on any person that is determined to operate in the oil sector of the Venezuelan economy.”

US sanctions prohibit most of the western world from doing business with either Tehran or Caracas, while also blocking the revolutionary governments from accessing national assets held outside of their borders.

Earlier this month, an Iranian passenger plane was forced to fly 1,000 kilometers on dwindling fuel supplies, after western suppliers refused to refuel the plane in fear of defying the White House.