Norwegian Air Shuttle’s Irish-based subsidiary, which finally won U.S. regulatory approval for low-cost flights between the U.S. and Europe on Friday, no longer is eyeing Boston’s Logan International Airport for its new direct service to Cork, Shannon and Dublin, Ireland.

Norwegian will choose between New Hampshire’s Portsmouth International Airport and T.F. Green Airport in Warwick, R.I., for Norwegian Air International’s nonstop flights aboard Boeing 737s, citing costs as the reason. The single-aisle 737 carries 150 fewer passengers than the Boeing 787 Dreamliner flights that Norwegian will continue to operate out of Logan.

“To operate the Boeing 737s … from a primary airport becomes much more expensive with a small aircraft type than a larger aircraft type due to limited passenger numbers,” Norwegian spokesman Anders Lindstrom said.

“These are the routes that will launch with $69 fares and have average return fares of $300 (to) $350, including taxes. In order to operate such flights profitably, they need to be served by medium-sized/smaller airports within the Greater Boston and NYC areas,” Lindstrom said.

Norwegian also opted to set up NAI’s New York base at Stewart International Airport in New Windsor, N.Y., rather than at the larger New York City airports.

The new U.S.-Ireland routes from New Hampshire or Rhode Island will launch next summer, with exact dates to be revealed early next year. The Cork, Shannon and Dublin flights are expected to operate four times weekly.

NAI will hire at least 70 people next year for its initial pilot and cabin crew base out of New Hampshire or Rhode Island.