A U.S. nuclear-powered aircraft carrier arrived in South Korea on Thursday in a demonstration of strength against North Korea, as the North’s leader reaffirmed his push to bolster ties with Russia.

The USS Ronald Reagan and its battle group came to the southeastern South Korean port of Busan after participating in a trilateral South Korean-U.S.-Japanese maritime exercise in international waters off a southern South Korean island earlier this week, the South Korean Defense Ministry said.

The aircraft carrier is to stay in Busan until next Monday as part of a bilateral agreement to enhance “regular visibility” of U.S. strategic assets to the Korean Peninsula in response to North Korea’s advancing nuclear program, according to an earlier Defense Ministry statement.

It’s the first arrival of a U.S. aircraft carrier in South Korea in six months since the USS Nimitz docked at Busan in late March, the statement said.