NEW YORK >> Tiny Allegiant Air is expanding its service again, this time with a focus on the East Coast.

The Las Vegas-based airline announced Tuesday that it is adding service to 10 new airports, including two on the far edges of the New York metropolitan area. It is also adding flights to Portsmouth, N.H., about an hour north of Boston.

Those markets represent a slight departure for the leisure-focused airline, which mostly flies from small, underserved cities to sunny vacation destinations. Allegiant will now serve 99 airports across the country, two more than Southwest Airlines, the largest domestic carrier. However, Allegiant generally only flies twice a week to most cities while Southwest has multiple daily flights.

Last year, 7 million passengers took a flight on Allegiant. That is a sliver of the 642 million people who took a domestic flight, including 134 million on Southwest.

Jude Bricker, Allegiant’s senior vice president of planning, noted that some of the cities added are “larger than what we’ve historically been focused on” but that the airline is trying to take advantage of service cuts in the east after the merger of AirTran and Southwest.

Most of the new flights will head to Florida.

Allegiant entices people who otherwise wouldn’t fly with low fares and non-stop flights. Then it aggressively pitches them hotels, rental cars, show tickets and other entertainment, earning millions in commissions.

Traditionally, it has focused on Las Vegas, but Bricker said that a $2.4 billion new terminal at McCarran International Airport there has increased the fees the airline pays to fly there by about $600 per flight, or $4 a passenger.

“We have to pass those costs on the customer,” Bricker said. “We’re still growing in Vegas but just very, very slowly.”

Bricker said the airline isn’t cutting service elsewhere but adding these routes thanks to seven new 177-seat Airbus A320s, which will be in service by year end. Each new plane allows Allegiant to open up four new cities.

The addition of Long Island MacArthur Airport, in Islip, N.Y. and Stewart International Airport, in New Windsor, N.Y., brings the airline closer to the lucrative New York market but still far enough away to avoid the region’s congestion and high prices. The other new cities are: Charlottesville, Va.; Clarksburg W. Va.; Concord, N.C.; Oklahoma City; Tulsa, Okla.; Syracuse, N.Y. and Manhattan, Kan.