NEW YORK (Reuters) - U.S. oil prices rose by 1 percent on Thursday, boosted by the U.S. threat of sanctions on Venezuela, but gains were capped by record high gasoline inventories and an unexpected big build in crude stocks in the United States.

FILE PHOTO: Oil takners pass through the Strait of Hormuz, December 21, 2018. REUTERS/Hamad I Mohammed/File Photo

U.S. West Texas Intermediate (WTI) crude futures rose 51 cents to settle at $53.13 a barrel, a 0.97 percent gain. Brent crude futures fell 5 cents to settle at $61.09 a barrel.

Washington signaled it could impose sanctions on Venezuela’s crude exports as Caracas descends further into political and economic turmoil. The threat to reduce supplies supported futures prices.

The United States, the top importer of Venezuelan crude, is seeking to ensure that the OPEC member’s oil revenue goes to opposition leader Juan Guaido, who swore himself in as interim president, and to cut off money from President Nicolas Maduro, a top U.S. official said on Thursday.

“The breakdown in diplomatic relations was interpreted as upping the possibility of a U.S. sanction on Venezuelan oil that would likely force U.S. refiners to seek alternative supplies at higher prices, hence the WTI gains,” Jim Ritterbusch, president of Ritterbusch and Associates, said in a note.

Venezuelan oil is predominantly heavy crude, which requires extensive refining. It is frequently blended with lighter crudes to give refiners higher-value products.

With Iran already crippled by U.S. sanctions, a drop in Venezuelan exports could squeeze global supply further.

Geneva-based Petro-Logistics said on its website that Iranian crude and condensate exports in December “fell steeply” from November to less than 1 million barrels per day (bpd) due to U.S. sanctions - lower than some other estimates.

Both Brent and WTI are both backed by light, sweet crudes, and are not directly linked to Venezuelan oil.

But concern about the supply of heavy crudes is apparent in the U.S. physical market, where the price for Mars Sour, a medium crude, shot to its highest since early 2011.

Two of the world’s biggest commodities trading houses, Glencore and Mercuria Energy Group, predict more oil price volatility in coming months due to concerns about supplies from Venezuela and Iran.

ANEMIC U.S. GASOLINE DEMAND

Weighing on oil futures, U.S. crude inventories sharply rose by 8 million barrels last week, the Energy Information Administration said on Thursday, versus forecasts for a decline of 42,000 barrels.

Gasoline stocks rose for the eighth straight week to a record 259.7 million barrels, as demand for the motor fuel over the past four weeks fell 0.1 percent from a year ago.

“The report was rather bearish, punctuated by the large crude oil inventory increase,” said John Kilduff, partner at Again Capital Management. “Gasoline demand remains anemic.”

Worries about the longer-term outlook for global economic growth, and therefore demand for crude, has pressured oil prices. Persistent concerns about the U.S-China trade war as well as slower world growth forecasts have kept investors wary.