Both countries viewed nuclear-powered submarine cooperation as strengthening South Korea’s defence role and the security alliance.

U.S. Under Secretary of Defense for Policy Elbridge Colby praised South Korea as a "model ally" during meetings with senior officials in Seoul on Monday.

The Pentagon's number three official hailed South Korea as a "model ally" as he met with local counterparts in Seoul on Monday, days after Washington's new defence strategy called for reduced support for partners overseas.

South Korea has placed overseas travel bans on three people as part of an investigation into alleged drone flights over North Korea that have deepened animosities between the rivals