HOUSTON (Reuters) - Venezuela's state oil company PDVSA has resumed regular imports of light crude as its own output of medium and light grades dwindles, creating bottlenecks for producing exportable blends, according to company documents and vessel tracking data.

U.S.-sanctioned Venezuela and Iran had a swap agreement that allowed PDVSA to import crude and condensate between 2021 and 2023 and use them as diluents for its heavy oil. But debts and disagreements over projects have stalled the exchange since last year, leaving the Venezuelan company with fewer options to source imports.

In December, a vessel carrying about 600,000 barrels of an unidentified imported light crude discharged at PDVSA's main terminal, Jose. Another tanker carrying a similar volume of light oil discharged at the same port last month, according to company shipping records seen by Reuters.

The Liberia-flagged vessel that discharged in January departed from China's Dongjiakou port, according to ship monitoring service TankerTrackers.com. But it was not immediately possible to identify the crude's origin.

PDVSA did not immediately reply to a request for comment.

The company increased exports in January to some 867,000 barrels per day (bpd) of crude and fuel, including almost 300,000 bpd to the United States, as the government of President Donald Trump warned about a possible cut in U.S. imports of Venezuelan crude.

The country's overall crude output rose slightly to 1.05 million bpd in January from 1.01 million in December, according to independent calculations.

However, PDVSA's long-standing struggles to provide enough diluents for its oil blending operations have worsened in recent months as output at Monagas North, a key region for producing the country's lightest crude grades, dwindles amid a lack of gas for reinjection into oilfields, sources close to operations said.

A key gas processing complex that had a major fire in November has not fully recovered supply to PDVSA's oilfields, the sources added.

Venezuela imported some 73,000 bpd of Iranian condensate and crude in 2022, which fell to about 40,000 bpd in 2023. Last year, PDVSA only made sporadic purchases of foreign crude cargoes, which averaged less than 15,000 bpd, according to LSEG vessel tracking data and company records.

As Venezuela's imports of foreign crude fell amid a less active trade with Iran, PDVSA's discharge of imported heavy naphtha from some of its joint-venture partners, including U.S. Chevron, has stabilized in recent years, contributing to fewer operational hiccups at the country's main output region, the Orinoco Belt.