US Secretary of State Antony Blinken arrived in Seoul late Wednesday in a show of support for a key Asian ally after North Korea ramped up military cooperation with Russia.

Blinken landed for his first visit to South Korea since President Yoon Suk Yeol took office last year. He flew straight from the G7 foreign ministers' meeting in Tokyo, which had followed Blinken's whirlwind tour of the Middle East.

The top US diplomat is expected to meet Yoon Thursday, as well as National Security Adviser Cho Tae-yong and his South Korean counterpart Park Jin, with the security implications of growing Moscow-Pyongyang military cooperation likely to top the agenda, US officials have said.

Kim Jong Un and Vladimir Putin held a summit in Russia's far east in September that was soon followed by repeated arms transfers, with Seoul saying Pyongyang had sent one million artillery rounds to further Moscow's war in Ukraine in exchange for advice on satellite technology.

"We're deeply concerned about what Russia is providing Pyongyang in return for the weapons and munitions that it's getting," Blinken said in Tokyo before flying to Seoul.

Russia and North Korea, who are historic allies, are both under a raft of global sanctions -- Moscow for its invasion of Ukraine and Pyongyang for its testing of nuclear weapons.

"The trip is the natural result of the G7 Foreign Ministers' meeting happening in Japan," Benjamin A. Engel, a professor at Seoul National University, told AFP.

"That said, the recent meeting between Kim Jong Un and Vladimir Putin made a high-level US visit to South Korea important."