WASHINGTON, June 17 (Reuters) - Oil refiner Tesoro Corp won approval from U.S. antitrust regulators to buy Northwest Products Pipeline system and related assets from Chevron Corp, on the condition it sells a petroleum terminal in Boise, Idaho. Tesoro struck a deal in December to buy the assets from Chevron for $400 million but lowered the price in May to $355 million after a renegotiation. As part of the deal, Tesoro bought the 760-mile pipeline, along with a series of terminals. The Federal Trade Commission said on Monday that with ownership of two of the three full service light products terminals the proposed transaction would have given the company too much power in the Boise market and therefore required the sale of one terminal. The FTC said it would allow Tesoro to close the transaction immediately, but sell the terminal within six months. In a separate transaction, Tesoro won antitrust approval in May to buy a BP refinery in southern California without being required to sell any assets. That transaction was worth $2.5 billion. Tesoro closed at $57.61 per share and Chevron at $121.22 on the New York Stock Exchange, each up 0.8 percent.