North Korea''s ballistic missile launches and nuclear tests will be a major topic of discussion during US Secretary of State Rex Tillerson''s trip to Asia this week, the State Department said.

Tillerson's trip comes a little more than a week after the government of Kim Jong-un carried out the launch of four ballistic missiles that landed in the Sea of Japan. The launch unnerved Asian nations, which now are scrambling for a plan on how best to confront the threat posed by the communist country.

Tillerson is scheduled to leave Washington today for Tokyo, where he will begin a three-country trip, his first to Asia since the former ExxonMobil chief executive became secretary of state. He will then travel to Seoul on Friday and Beijing on Saturday.

"This trip will allow Secretary Tillerson to engage allies and partners on not only a range of bilateral issues, but also importantly to discuss and coordinate strategy to address the advancing nuclear missile threat from North Korea," said Acting Assistant Secretary of State Susan Thornton.

The United States is committed to holding North Korea accountable for its "flagrant and repeated disregard of UN Security Council resolutions, which explicitly prohibit ballistic missile and nuclear programmes," she said, speaking at a briefing in Washington.

Tillerson is scheduled to meet in Seoul with South Korean Prime Minister Hwang Kyo-ahn, who became acting president after the impeachment of president Park Geun-hye, and Foreign Minister Yun Byung-se.

'US intent on keeping up the pressure'

Thornton said the US is "intent on keeping up the pressure on the North Korean regime" with a goal to "change the calculus" to try to get North Korea back to the negotiating table. She didn't expect anything new to be announced during the trip, but said "discussing the elements of any new approach will be an important part of the discussions".

The United Nations has implemented several rounds of sanctions against North Korea over the past decade in response to its missile launches and nuclear programme, but to no avail.

Last year North Korea launched 21 ballistic missiles and carried out two nuclear tests. It has launched five missiles this year. The most recent, Pyongyang said, were in response to an annual US-South Korea military exercise.

China remains North Korea's only major ally and trading partner, but relations between the two countries are at a low. Tillerson will walk a fine line in Beijing in part because China is not pleased with US efforts to strengthen South Korea's defences with a missile defence system for South Korea.

Beijing fears that the systems could be used to keep China in check, but the US says the Terminal High-Altitude Area Defense (THAAD) system is strictly defensive.

"The way we look at the THAAD deployment is, it's a very utterly reasonable step for a country to take when it sees itself threatened by its northern neighbour," Thornton said.

In Tokyo, Tillerson will meet with Prime Minister Shinzo Abe and Foreign Minister Fumio Kishida. His Beijing meetings will be with Chinese President Xi Jinping and Chinese Foreign Minister Wang Yi.

Tillerson will stress the goal of developing a "results-oriented relationship" with China and press Beijing to abide by international rules and norms, Thornton said.

- dpa