TOKYO -- SoftBank Group's search for a partner for U.S. wireless unit Sprint has borne little fruit so far, with candidates inside and outside the industry proving unreceptive to the Japanese technology giant's overtures.

SoftBank's top target is fellow wireless carrier T-Mobile US, which SoftBank Chairman and CEO Masayoshi Son has called the best potential merger partner. Son tried to engineer a merger between the two back in 2013, after SoftBank's $21.6 billion acquisition of Sprint, and has recently resumed his pursuit.

Combining No. 3 T-Mobile and fourth-place Sprint would create an entity large enough to challenge the duopoly of Verizon Communications and AT&T. It would also save the two rivals the trouble of competing for the same customer base.

But informal talks toward a merger have apparently gone nowhere. T-Mobile has more subscribers than Sprint, thanks to an aggressive marketing strategy, and parent Deutsche Telekom has repositioned the carrier as a core business.

Faced with this impasse, Sprint put the idea on the back burner to hold talks with Charter Communications and Comcast on a deal to let the cable companies resell Sprint's wireless service. The carrier likely hoped to strengthen its hand in the T-Mobile negotiations by bringing the two big newcomers to the wireless industry into its orbit.

The exclusivity period for the Charter and Comcast talks ended last week with no agreement reached. Whether Sprint can negotiate a good deal in extended discussions remains to be seen.

The Wall Street Journal reported late last week that Sprint proposed a merger with Charter, an offer since rebuffed by the cable company. A SoftBank executive denied that any such approach was made. Son is also said to be considering a bid to buy Charter outright instead. Reuters reported back in February that SoftBank would even be willing to cede control of Sprint to facilitate a merger with T-Mobile.

On top of this, SoftBank is apparently exploring the possibility of a merger between Sprint and satellite TV company Dish Network.

The U.S. wireless industry is central to SoftBank's plans for the coming "internet of things" era. America is a leading adopter of the technology, and a nationwide wireless network like Sprint's could be put to use as infrastructure.

"Letting go of Sprint is not an option -- this consolidation [push] is an offensive measure," a SoftBank executive asserted.

Meanwhile, SoftBank's efforts over the past few years to whip Sprint's finances into shape via deep cost cuts and investment in its wireless and sales networks are finally paying off. Sprint reported a $206 million net profit for the April-June quarter Tuesday, marking its first quarter in the black in three years. Earnings per share came to 5 cents, trouncing analysts' forecast of a roughly 1-cent loss.

Revenue rose 2% to $8.15 billion. The company added a net 88,000 postpaid phone subscribers thanks to cut-rate wireless plans.

Nikkei staff writer Tamami Shimizuishi in New York contributed to this article.