BEIJING, CHINA:China Unicom's move to deepen ties with Spain's Telefonica could add pressure on its domestic rivals to seek similar tie-ups as they build out complex 3G networks following an industry restructuring.

China's telecom carriers are all trying to chart their courses after the overhaul early this year that saw the country's four main carriers reduced to three, each tasked with building a third generation (3G) mobile network.

As part of the revamp, two of the four previous companies were merged to form China Unicom. Telefonica and SK Telecom had held separate stakes in those two companies, bringing the Spanish and South Korean companies together as unusual bedfellows in the merged firm.

Telefonica's move to boost its stake in China Unicom to 8 percent, which was announced on Sunday , represents a reaffirmation of the company's commitment to the Chinese firm, analysts said.

SK Telecom, which still owns about 3.8 percent of Unicom, is still studying Telefonica's move and had no official reaction, said spokeswoman Lauren Kim.

SK Telecom's shares were down 2.88 percent in Korea, compared with a small drop for the broader market, while Unicom's shares were up 2.42 percent, versus a 1.57 percent rise for the broader Hang Seng index .HSI.

China's dominant wireless carrier, China Mobile, has its own longstanding equity ties with Europe's Vodafone, while the country's third major carrier, China Telecom, has no major foreign equity partners.

Despite making headlines at the time of their announcement, none of the stake purchases has produced any major collaborations. Analysts said they did not expect that to change in the near term for Telefonica, following the strengthened bond with Unicom.

"The relationship is at the strategic level," said Yuanta Securities' Shu Ming. "But Unicom still has lots of work to do before we see anything significant from this."

Still, the tie-up could put pressure on China Telecom to find a partner, since it has the least experience building and operating a mobile network, analysts said.

"All of this is a continuing shake-out from the recent organisation, and there may be other similar transactions in the near future amongst the other operators," said an industry consultant who spoke on condition of anonymity because he has worked with some of the players.

All three Chinese carriers are facing intensifying competition following last year's reshuffle, even as they are spending a total of $58.5 billion through 2011 on 3G networks.

The Telefonica-Unicom deal could nudge SK Telecom toward China Telecom, because the two firms both use the same 3G technology.

"SK Telecom might be more interested in China Telecom now," said Steven Liu, an analyst at DBS Vickers.

SK Telecom works with both the world's widely used 3G wireless standards -- WCDMA, which Unicom is developing, and China Telecom's CDMA200.