US and South Korea deepen cooperation on nuclear submarine plan

Ahn also pressed for faster progress on the transfer of wartime operational control to Seoul and called for closer coordination on alliance follow-up measures, the ministry said.

Colby, the Pentagon's top defence and foreign policy official, said in a post on social media on his arrival that South Korea is a "model ally" committed to increasing defence spending in line with US regional strategy.

South Korea hosts about 28,500 US troops and last year pledged to lift defence spending to 3.5 per cent of GDP, a move that Colby and other US officials have praised as strengthening Seoul's role in deterring North Korea.

Colby will also visit Japan during his Asian trip, according to media reports.

(Reporting by Kyu-seok Shim Editing by Ed Davies)