Warships from US, South Korea and Japan will simulate detecting potential ballistic missiles from North Korea as tensions rise in the region over Pyongyang's fast-developing weapons programmes.
The US, South Korea and Japan started joint exercises on Monday to track missiles from North Korea, Seoul's military said, following the nuclear-armed Pyongyang's longest-range test launch to date.
The trilateral drill comes less than two weeks after Pyongyang test-fired a new intercontinental ballistic missile (ICBM) and declared it had achieved nuclear statehood, escalating global alarm over its weapons push.
The two-day exercise – the sixth since June last year – kicked off in waters near the Korean peninsula and Japan, Seoul's defence ministry said.
"During the drill, Aegis warships from each country will simulate detecting and tracking down potential ballistic missiles from the North and sharing information," it said in a statement.
Two US ships are taking part, with one each from the two Asian countries.
Both South Korea and Japan have security alliances with the US, although their own relationship is marred by disputes over history and territory.
Washington and Seoul staged their biggest-ever joint air drill last week in a show of force against Pyongyang, which is subject to multiple sets of UN sanctions over its ballistic missile and nuclear weapons programmes.
Tension flared anew in the flashpoint peninsula after the November 29 launch of the Hwasong-15 ICBM, which the North claimed could deliver a "super-large heavy warhead" anywhere on the US mainland.
Many analysts suggest that the rocket is capable of reaching the US mainland but voiced scepticism that Pyongyang has mastered the advanced technology needed to allow the rocket to survive re-entry to the Earth's atmosphere.
Last month's launch was the first test of any kind since September 15 and quashed hopes that the North may have held back in order to open the door to a negotiated solution to the nuclear standoff.
South Korea imposes sanctions on North Korea
The South condemned the launch and on Monday and added several North Korean groups and individuals to a sanctions list to cut off funding for the North's weapons programs.
The government said those added were 20 North Korean groups, including several banks and companies, and 12 individuals.
Seoul is among the first to respond to North Korea's November 29 missile launch with fresh sanctions. While the move is largely symbolic because all transactions between two Koreas have been banned for years, the government said it hopes its move will prompt the international community to do likewise.
The blacklist includes Rason International Commercial Bank and Korea Zinc Industrial Group. Individuals are North Korean officials who work for the country's banks or companies based in China, Russia, Vietnam and Namibia.