Gap Inc, the US' largest specialty clothing retailer, is to expand its customer base into a new retail sector after buying women's sports and active apparel company Athleta Inc for $150m in cash.

"This strategic acquisition complements our brands perfectly and allows us to leverage our new online platform to expand into this significant retail sector," said Glenn Murphy, Gap Inc's chairman and CEO.

"Athleta is a great success story with loyal customers that will now become part of the Gap Inc family of brands."

Following the acquisition, Athleta will become the "fifth tab" on Gap's online platform, called Universality, which allows shoppers to browse and buy from all of the company's brands in one shopping cart with a single shipping fee.

Athleta's products will be ultimately sold online alongside those from Gap, Banana Republic, Old Navy and Piperlime.

Founded 10 years ago and based in based in Petaluma, California, Athleta has evolved into a lifestyle brand that offers apparel for a variety of sports, including yoga, running, skiing, snowboarding and surfing through its catalogues and internet site.

Joe Teno, the current CEO of Athleta, will remain as president of Athleta at Gap Inc upon the completion of the deal. He will report to Toby Lenk, the president of the Gap Inc Direct division.

"We're thrilled to become part of this great company and to have found a partner that supports our vision for Athleta," Teno said.

San Francisco based Gap sees the deal as enhancing its foothold in the growing $31bn women's active apparel sector in the United States.

In particular, it will allow the firm to tap into popular athletic activities such as yoga and pilates, where customers are demanding stylish yet functional clothing.

This sector has already provided huge growth opportunities for brands such as Lululemon, Under Armour, Prana and Nike.

It will also build on the success of Gap's online sales, which have been outpacing those at the company's stores.

In the retailer's second quarter results published last month, same-store sales fell 6% at the Gap North America, Banana Republic North America and International divisions, while Old Navy North America was down 16%.

In contrast, however, the company's online sales rose 11% to $191m.

Gap, which runs 3,170 stores, may also see an opportunity to open Athleta branded stores, expanding the line's current catalogue and online base.