By Hyonhee Shin and Hyunsu Yim
SEOUL (Reuters) -U.S. Secretary of State Antony Blinken said a North Korean missile test carried out during his visit to Seoul on Monday was a reminder of the need to deepen Washington's cooperation with South Korea and Japan to deter an emboldened Pyongyang.
North Korea fired what appeared to be an intermediate-range ballistic missile at around noon (0300 GMT), which flew more than 1,100 kilometres (690 miles) east before falling into the sea, according to South Korea's military.
Speaking a few hours later, Blinken told a news conference the launch underscored the importance of collaboration between the U.S., South Korea and Japan, including on sharing real-time missile data and holding trilateral military exercises.
"Today's launch is just a reminder to all of us of how important our collaborative work is," he said.
Blinken also warned of Pyongyang's deepening ties with Moscow. He said Washington believed Russia intended to share space and satellite technology with North Korea in exchange for its support for the Ukraine war, in which more than 1,000 North Korean soldiers have been killed or wounded.
President Joe Biden, who leaves office this month, made headway in deepening trilateral cooperation between the U.S. and South Korea and Japan, despite historic issues that have often plagued relations between the Asian neighbours.
But political turmoil in South Korea, together with the imminent return of the unpredictable rule of Donald Trump in the United States, has raised questions over whether those efforts can be sustained.
South Korean lawmakers last month voted to impeach President Yoon Suk Yeol and suspend him from duties after his Dec. 3 declaration of martial law stunned the country. Yoon's impeachment trial is being heard by the Constitutional Court.
If Yoon is permanently removed from office, a presidential election would be called and the liberals -- seen as likely to win that contest -- have been critical of Yoon's efforts to partner with Tokyo.
Blinken, who also met on Monday with acting President Choi Sang-mok, told the news conference that while Washington had "serious concerns" about Yoon's actions, it had confidence in the country's institutions and democratic resilience.
Monday's launch was Pyongyang's first since Nov. 5 when it fired at least seven short-range ballistic missiles.
It was not immediately clear what type of missile was fired but North Korea's IRBM tests last year featured a new solid-fuel design and carried what Pyongyang said was a hypersonic glide vehicle, a warhead designed to be able to manoeuvre and evade missile defences.
The North has said it is working to make its missiles of all ranges solid fuel. Solid-fuel missiles do not need to be fuelled immediately ahead of launch, are often easier and safer to operate, and require less logistical support, making them harder to detect and more survivable than liquid-fuel weapons.