UPDATE 1-Citgo Petroleum's new board members arrive in Houston headquarters

(Adds details on board members, context)

Feb 21 (Reuters) - Members of boards of directors appointed this month by Venezuela's opposition-controlled congress to run state-owned oil firm PDVSA's U.S. subsidiaries arrived at Citgo Petroleum's Houston headquarters, two people familiar with the matter said on Thursday.

Venezuela's National Assembly, led by opposition leader and self-proclaimed president Juan Guaido, last week appointed new boards for PDVSA and its subsidiaries PDV Holding, Citgo Holding and Citgo Petroleum amid a political battle to control the country's foreign assets.

Citgo Chairwoman Luisa Palacios and other members of the new board have been working with advisers to legally assume control of the company in Delaware, where the U.S.-based refiner is registered, according to people familiar with the matter.

On Thursday, Palacios was working from Citgo's CEO office, according to one of the people. It was unclear on Thursday if she plans to take the CEO title.

Citgo did not respond to several requests for comment. Since the United States imposed sanctions on PDVSA on Jan. 28, the unit has not disclosed executive changes or its stance on the new board of directors.

Four top Citgo executives were removed from their posts this week. The four were linked to the previous board, led from a Caribbean office by Asdrubal Chavez, a cousin of Venezuela's late President Hugo Chavez that was appointed by Socialist President Nicolas Maduro in 2017.

Citgo is the eighth-largest U.S. refiner and owns plants in Illinois, Texas and Louisiana that provide about 4 percent of U.S. refining capacity. It also operates pipelines and terminals, and supplies fuel to a retail network of 5,000 gas stations across 30 U.S. states. (Reporting by Marianna Parraga; Editing by Gary McWilliams, Chizu Nomiyama and Susan Thomas)