HOUSTON, Sept 14 (Reuters) - Venezuelan crude sales to the United States declined almost 13 percent last month to 712,870 barrels per day (bpd) due to fewer shipments of crude blends and upgraded oil from the Orinoco Belt, according to Thomson Reuters trade flows data.

Venezuela’s crude output has significantly declined this year amid a longer-than-expected cycle of low prices, affecting exports to state-run PDVSA’s main customers, including companies in the United States.

PDVSA and its joint ventures sold 43 crude cargoes to the U.S. in August. Main receiver was its own unit Citgo Petroleum, followed by refining firms Valero Energy and Phillips 66 .

Separately, refiners Axeon Specialty Products and PBF Energy made spot purchases of Venezuela’s diluted crude oil (DCO), Boscan and Hamaca crudes.

The August exports volume also marks a 12 percent decline versus the 808,000 bpd sold in the same month of 2015.

Lack of imported oil enough to dilute extra heavy crude output has impacted operations at the Orinoco Belt in recent weeks, according to traders and sources from PDVSA’s joint ventures.

The most recent cargo of the heavy naphtha PDVSA imports to mix with Venezuelan oil discharged at Jose port in mid-August, according to Reuters data.

Long payment delays have also prevented BP from allowing discharge of four cargoes carrying some 2.7 million barrels of U.S. light crude that are currently anchored around the island of Curacao. One of them has been moored since mid-June. (Reporting by Marianna Parraga; Editing by Marguerita Choy)