Venezuela's state oil company PDVSA has canceled several authorizations it had granted to its joint venture partner, Chevron, to load and export Venezuelan oil this month, three sources with knowledge of the decision said on Thursday.

Chevron Corp. was ordered to return nearly 1 million barrels of Venezuelan oil to Petroleos de Venezuela SA in a blow to the oil major, which was working to secure crude before wrapping up operations in the country when a US sanctions deadline hits in May.

Chevrons Venezuelan crude shipments have hit a roadblock as PDVSA, Venezuelas state oil company, revoked export authorizations for several tankers due to payment uncertainties linked to renewed U.S. sanctions.