Kacper Pempel/Reuters

LONDON – Nokia agreed on Monday to buy Siemens’s half of a telecommunications equipment joint venture for about 1.7 billion euros ($2.2 billion) as Nokia continued to struggle with challenges in its core business.

Once the reigning handset maker, Nokia has failed to maintain market share, particularly for smartphones, in the face of competition from Apple’s iPhone and a tide of phones from Samsung and others that run on Google’s Android operating system.

By acquiring the 50 percent stake in Nokia Siemens Networks that it does not already own, analysts said Nokia had secured ownership of a profitable business to prop up its balance sheet, as it continued efforts to turnaround its cellphone operations.

“This increases the range of strategic options Nokia has in the future,” Janardan Menon, a telecommunications analyst at Liberum Capital, wrote in a research note on Monday. “Nokia is acquiring this asset at a very attractive price, well below what an I.P.O. or trade sale could bring in the future.”

Under the terms of the deal, Nokia said it would pay 1.2 billion euros to Siemens for the joint venture, and 500 million euros in the form of a secured loan from the German company that must be repaid one year after the transaction is completed.

Nokia’s chief executive, Stephen A. Elop, suggested that while Nokia was purchasing all of Nokia Siemens, the agreement might be an intermediate step toward a potential sale of the equipment venture.

The company has no plans to integrate Nokia Siemens into its existing operations, and the venture will remain a separate entity with its current management, Mr. Elop told reporters on a conference call on Monday.

“As the deal is closed, we will continue to strengthen N.S.N. as a more independent entity,” Mr. Elop said. “As for the future for Nokia Siemens, we have consistently said that there are a range of options available.”

Investors have interpreted Mr. Elop’s comments to mean that Nokia may be prepared to sell all or part the business to a single buyer, or to investors through an initial public offering. With 4.5 billion euros in net cash on hand at the end of the first quarter, Mr. Elop said the timing was now right to complete the deal.

“Economically, the transaction somewhat stands on its own,” he said. “We felt that the purchase was very attractive for Nokia’s shareholders, its customers and its employees.”

Nokia’s share price jumped by more than 8 percent in afternoon trading in Helsinki, Finland, on Monday, while shares of Siemens rose 2.2 percent in Frankfurt.

The agreement comes as little surprise. Siemens had indicated that it wanted to divest its stake to focus on its industrial and energy operations. And an agreement binding Nokia and Siemens together expired in April, freeing both to explore potential deals for their holdings.

Siemens reportedly had held discussions with private equity firms about selling its stake. The company is selling or spinning off several business units, including its solar power division, to focus on profitable areas like transportation and health care.

“With this transaction, we continue our efforts to strengthen our focus on Siemens’ core areas of energy management, industry and infrastructure,” Joe Kaeser, the chief financial officer of Siemens, said in a statement.

Nokia Siemens, which has roughly 60,000 employees worldwide, was created in 2007 through the combination of the network infrastructure businesses of Nokia and Siemens. The unit provides for services for both fixed-line and mobile networks.

After a major restructuring, Nokia Siemens has slowly improved its profitability. A campaign to cut expenses and focus on next-generation wireless data technology has paid off, as the venture reported a pro forma operating profit of 822 million euros last year, up 145 percent from the previous year. It ended the year with about 1.3 billion euros in net cash.

Nokia Siemens now claims about 20 percent of the market for the latest generation of wireless data networks, commonly known as Long Term Evolution, or LTE.

The deal for Nokia Siemens is expected to close during the third quarter of this year.

Kevin O’Brien contributed reporting from Berlin.