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By Arathy Somasekhar

HOUSTON, April 10 (Reuters) - Venezuela's state oil company PDVSA has canceled several authorizations it had granted U.S.-based producer Chevron CVX.N to load and export Venezuelan crude in April, three sources with knowledge of the decision said on Thursday.

The cancellations follow U.S. President Donald Trump's imposition of tariffs on Venezuela's oil buyers. The suspensions also comes after Washington canceled key licenses last month to a handful of PDVSA partners and customers, including Chevron, that had allowed them to operate and export Venezuelan oil under exemptions to the U.S. sanctions on the South American country.

The U.S. Treasury Department gave the companies until May 27 to wind down operations and complete purchases. Chevron was exporting about 250,000 barrels per day (bpd) of Venezuelan crude to the U.S. under its license.

In early April, Washington imposed a 25% tariff on buyers of Venezuelan crude and gas, a measure experts said could hurt China the most.

Two of the cargo cancellations by PDVSA involve tankers that had already loaded, so the oil would have to be returned to ports, while a third had not loaded, one of the sources said.

PDVSA and Chevron did not immediately reply to requests for comment. It was not immediately clear if the cargoes would be rescheduled.

The government of Venezuelan President Nicolas Maduro on Thursday again rejected the U.S. measures. Officials have said they amount to an "economic war".

The tariffs on Venezuela's oil buyers earlier this month prompted the temporary suspension of some cargo loadings, particularly those bound for China, which is the largest recipient of Venezuela's oil. But the loadings were resuming this week.

Chevron, whose exports of Venezuelan crude were not affected by the tariffs because of its license, had not been impacted by the measures until now, according to the sources and shipping data showing tanker movements.

(Reporting by Arathy Somasekhar; Editing by Sandra Maler and Christian Schmollinger)

((marianna.parraga@thomsonreuters.com; +1 713 371 7559; Reuters Messaging: @mariannaparraga))