(Adds details on halt, possible sale or partners)
SAO PAULO, Dec 14 (Reuters) - Spanish conglomerate Abengoa told Brazil's power sector regulator Aneel that it has stopped work on concessions to build and operate new transmission lines in the country, according to a document seen by Reuters on Monday.
The document, obtained with a freedom of information request, detailed Aneel's recent meeting with Abengoa executives, who confirmed the stoppages on construction sites.
Unions representing construction workers, a wind power industry group and Abengoa's subcontractor on the power lines had told Reuters last week that the company informed them of the interruption.
Abengoa has not responded to requests for comment.
The troubled company, which filed for bankruptcy protection last month in Spain, also told Aneel that it is in talks to sell the transmission concessions or find partners to help it proceed with construction.
The stoppage could become a serious setback for Brazil's efforts to emerge from its worst energy crisis in 14 years.
Abengoa holds concessions to build and operate 6,300 kilometers (3,900 miles) of transmission lines in Brazil that are vital to connecting dozens of wind farms to the grid.
It is also due to construct a line carrying power from the word's third-largest hydroelectric power dam, Belo Monte, in the Amazon state of Para, to Brazil's power-hungry northeast region starting in August.
Brazil's Aneel said in the meeting minutes it had asked the Spanish company to send weekly updates on the situation.
The timing of an asset sale may be tough for Abengoa, as interest rates are climbing in Brazil amid a severe economic crisis, making infrastructure investments tougher to finance.
In a Nov. 18 auction for concessions to build and operate power lines, the government sold only four out of 12 available lots. (Reporting by Luciano Costa and Marcelo Teixeira; Editing by Bernard Orr)