Tillerson will meet for the first time with South Korea's acting president, Prime Minister Hwang Kyo-ahn, who is obliged to call new elections within 60 days.

Other factors complicating the secretary of state's discussions in Seoul and Beijing are the complex political situation in South Korea, which has just impeached its president, and China's resentment about the deployment in South Korea of a controversial U.S. defensive missile system.

Pyongyang's provocative gestures, such as firing multiple missiles into the Sea of Japan this month, have been so strident that Washington said it is "moving farther away" from considering the option of a direct engagement with the North Koreans and their mercurial young leader, Kim Jong-un.

U.S. Secretary of State Rex Tillerson, making his first trip to Japan, South Korea and China as the top United States diplomat this week, is expected to expand the effort to find new options for dealing with North Korea and the nuclear and military threat it poses to the region and to the world.

◆ Close Partners in South Korea

A senior State Department official told reporters in an advance briefing the United States will continue to work with Hwang for the remainder of his tenure, and added that Tillerson would not be meeting with opposition factions in Seoul.

"What we're seeing play out now is a manifestation of the democratic process in South Korea. This is the kind of institution that makes us such close partners, and friends with people in South Korea," the senior official said.

"The United States continues to be a steadfast ally, friend, and partner to [South Korea]. The U.S.-[South Korea] alliance will continue to be a linchpin of regional stability and security," she added.

◆ 'Reach out to all sides'

"Tillerson should make every effort to reach out to all sides in South Korea that have a vested interested in a strong [South Korea]-U.S. alliance," Harry Kazianis of the Center for the National Interest told VOA.

"This is the only way to ensure that if Seoul in the near future does seek a détente with Pyongyang, which is very possible under a more leftist government, America and South Korea can work together to coordinate policy and take some sort of joint approach," he added.

The United States has also become embroiled in a dispute with China over the deployment of a controversial American missile-defense system in South Korea.

The first elements of the U.S. Terminal High Altitude Area Defense missile system, known as THAAD, arrived in South Korea last week, one day after North Korea launched at least four ballistic missiles in rapid succession, sending the rockets over the Sea of Japan, within 350 kilometers of Japanese territory.

◆ U.S.: THAAD Is No Threat to China

Washington said the proximity of those events demonstrated the U.S. action was defensive in nature, and intended exclusively to counter the threat from Pyongyang.

"We've been very clear in our conversations with China that this is not meant to be a threat. Not a threat to them or any other power in the region. It is a defensive system," Mark Toner, the State Department's acting spokesperson, has told reporters.

Nevertheless, Beijing has strongly opposed deployment of the advanced U.S. weapons system near its borders, declaring THAAD is an unnecessary and provocative military escalation. The basis of China's opposition is its military leaders' belief the powerful radar the U.S. system uses to track missiles launched by North can also look deep into China.

"I believe that they will sustain this pressures during the next few months, in the hope the new leader of South Korea can be convinced to reverse the decision," said Dennis Wilder, an adviser to former President George W. Bush and currently a senior fellow at Georgetown University's U.S.-China Initiative.

◆ Groundwork for Xi's Trip to U.S.

In China, where Tillerson will meet with President Xi Jinping, one of his primary tasks is preparing for a visit to the United States by the Chinese leader expected later this year.

Washington is intent on pursuing a constructive relationship with China, while remaining determined to ensuring that China abides by international rules, and that trade between the two countries is conducted on a so-called level playing field -- under conditions that favor neither side unfairly.

Wilder of Georgetown's U.S.-China Initiative told VOA that Chinese officials "will be looking for indications of how seriously President Trump will pursue economic issues such as redressing the trade balance and seeking more opportunities for U.S. firms to export goods and services to China."

