Dec 2 (Reuters) - Venezuela's oil exports almost doubled in November from the previous month as new customers linked to a Russian trading firm stepped in to boost purchases from state-run PDVSA amid U.S. sanctions, according to data from the firm and Refinitiv Eikon.

In October, PDVSA's established customers suspended swaps of Venezuelan crude for fuel at Washington's request, leading to a sharp decline in exports, but in November a growing group of new buyers stepped in to bring Venezuela's exports back to around the average level for this year, the data showed.

A total of 24 cargoes left Venezuelan waters last month carrying some 639,000 barrels per day (bpd) of crude and refined products, according to the data, an increase from the 360,000 bpd exported in October.

Their main destination was Asia, where trans-shipment of Venezuelan crude between tankers at sea frequently occurs before the oil reaches its final destination, principally China.

More than half of Venezuela's exports in November were received by new buyers including Xiamen Logistic Grass, Olympia Stly Trading, Zaguhan & Co, Karaznbas, Kalinin Business International and Poseidon GDL Solutions, the data revealed.

These customers were registered in Russia this year by Moscow-based OGX Trading.

Most vessels chartered by these companies navigated to Venezuela with their transponders disconnected, a technique known as a "dark voyage". They have switched their signal on again after departing, the Eikon data showed.

A handful of them were also misidentified by PDVSA using the names of scrapped tankers, according to its loading schedules.

PDVSA and Venezuela's oil ministry did not immediately reply to requests for comment. OGX Trading told Reuters in late October the company had been unable to start business due to the coronavirus.

Click here for a graphic on Venezuela's monthly oil exports during 2020: https://graphics.reuters.com/VENEZUELA-OIL/EXPORTS/xegpbqdzjvq/

The November exports also included two large cargoes of heavy crude taken by a firm called Cirrostrati Technology Co LTD onboard two tankers owned by state-run PetroChina.

Meanwhile, exports to Cuba - a close ally of Venezuela - declined to 47,300 bpd, from 104,000 bpd in October.

As oil exports in November returned to this year's average of around 650,000 bpd, Venezuela's fuel imports declined sharply to 21,000 bpd after two diesel cargoes were delivered by India's Reliance Industries to PDVSA before winding down its trade with Venezuela.

Imports by the gasoline-thirsty nation were 100,500 bpd in October.

(Reporting by Marianna Parraga in Mexico City and Mircely Guanipa in Maracay, Venezuela Editing by Marguerita Choy)