The United States on Monday reiterated its "ironclad" security commitment to South Korea as tensions flared anew following North Korea's recent test-firing of a claimed submarine-launched cruise missile.

The North's Korean Central News Agency reported Monday that North Korean leader Kim Jong-un oversaw the test-fire of the newly developed SLCM and reviewed a project to build a nuclear-powered submarine the previous day.

"We are monitoring these activities and we won't comment on intelligence," Deputy Pentagon spokesperson Sabrina Singh told a press briefing.

"We've been very clear on the threat posed by the DPRK and their military programs and our commitment to the Republic of Korea and Japan continues to be ironclad," she added.

Singh also commented on Russia's reported warning against South Korea's support for Ukraine.

"You see countries all around the world supporting Ukraine's cause and the fight for their democracy and the fight for their sovereign territory," she said.

She added, "You are seeing like-minded nations like the United States and other countries, stand in alliance in support of a democracy and in support of a sovereign country who was unjustly invaded by its neighbor. And we are very proud of the coalition that we've built in support of Ukraine." (Yonhap)