After talks with his South Korean counterpart Tuesday, U.S. Secretary of State John Kerry said Washington and Seoul “stand very firmly united without an inch of daylight between us” in dealing with North Korea’s nuclear and ballistic missile programs and proliferation activities. He said the allies would continue to modernize their capabilities to face any threat from the North.

Kerry’s remarks seemed to reflect Washington’s recent focus on portraying its strong alliance with Seoul as a stabilizer in the Northeast Asian situation, which is becoming increasingly volatile amid China’s rise, North Korea’s internal shake-up and Japan’s shift to unbridled right-wing nationalism.

In a press release issued after Monday’s meeting between U.S. Defense Secretary Chuck Hagel and visiting South Korean Foreign Minister Yun Byung-se, the Pentagon said Hagel reaffirmed the crucial role of the alliance, which “serves as a linchpin for peace and stability in the Asia-Pacific region.” Around the same time, Seoul’s Defense Ministry announced the U.S. Army would deploy a mechanized infantry battalion made up of advanced battle tanks to South Korea to bolster deterrent capability on the peninsula as part of a rotational force.

These U.S. moves are encouraging for Seoul, which has been bracing for any possible provocation from the North in the aftermath of the execution of the regime’s No. 2 figure and is uneasy with Washington’s support for Japan’s military buildup and assertions of a right to collective self-defense.

To help place the alliance on a firmer footing, the two sides need to facilitate talks on sharing the cost of stationing U.S. troops here and smooth out differences over setting up a missile defense system and renewing an accord on nuclear energy cooperation. Strengthening the bilateral alliance with the U.S. may not necessarily be incompatible with South Korea’s efforts to expand its strategic partnership with China. But forging three-way security cooperation with Japan as Washington hopes to do is a more sensitive matter. Japanese Prime Minister Shinzo Abe’s nationalistic steps, including his recent visit to a controversial war shrine in Tokyo, have complicated U.S. efforts. Still, it will and should remain on Seoul’s to-do list to strengthen coordination with Washington and Tokyo over North Korea issues.