TAOYUAN, Aug 18 (Reuters) - Taiwan Vice President William Lai returned on Friday from a sensitive visit to the United States, thanking the Taiwanese people for supporting a trip he said showed the island's "self confidence" venturing into the international community.

"Because of everyone's hard work, Taiwan's power is stronger and stronger, and it showed the international community that Taiwan is a force for good, that the international community really pays great attention to Taiwan," he said.

China claims Taiwan as its territory and denounced the transit stops in the U.S., calling Lai a separatist and a "troublemaker".

Lai officially only made transits in the United States, first in New York and then in San Francisco, on his way to and from Paraguay to attend the new president's inauguration in one of only 13 countries that maintains formal ties with Taipei.

While in the United States, he gave speeches to the Taiwanese community and met officials from the American Institute in Taiwan (AIT), a U.S. government-run non-profit that handles unofficial relations.

Taiwanese officials have said China is likely to conduct military exercises this week near the island, using Lai's U.S. stopovers as a pretext to intimidate voters ahead of next year's presidential election and make them "fear war".

Lai is frontrunner to be Taiwan's next president at elections set for January. President Tsai Ing-wen cannot run again after two terms.

China especially dislikes Lai because of comments he has previously made about being a "practical worker for Taiwan independence", though he has pledged on the campaign trail to maintain the status quo and offered talks with Beijing.

Speaking at Taiwan's main international airport at Taoyuan after stepping off his flight, Lai made only passing mention of his U.S. stopovers, concentrating instead on Paraguay and pledges of support he received there.

"Thank you for your contributions to the country and to society," he said, "allowing Taiwan to very progressively, self confidently and respectfully go into the international community, and winning the support of the international community."

Taiwan has no far not reported any unusual Chinese military movements near the island.

However, on Thursday Japan's government reported 11 Chinese and Russian naval ships, including destroyers, had crossed waters between the southern Japanese islands of Okinawa and Miyako, a waterway crucial to access to the Pacific and East China Seas.

The islands lie directly to the east of Taiwan and Okinawa is home to a major U.S. military base.