South Korea's military said on Monday that a US aircraft carrier is about to arrive in South Korea, after North Korea fired two short-range ballistic missiles into the sea off its east coast.
The missiles were fired from North Hwanghae province on Sunday at 7: 47 a.m. 2247 GMT and south Korea's Joint Chiefs of Staff JCS said about 370 kilometres 230 miles.
According to the Japanese government, both missiles appear to have landed outside Japan's exclusive economic zone.
South Korea's military strongly condemned the launches as a grave provocation against the United Nations Security Council resolutions and called for an immediate halt.
We will keep a close eye on North Korea's various activities and maintain a firm readiness posture based on the ability to respond to any provocations, the JCS said in a statement, adding that it would continue military drills with the US as planned.
The Japanese government has also protested against North Korea, saying its missile launches threaten the safety and peace of Japan, the region and the international community.
Monday's launches came after the US aircraft carrier USS Nimitz and ships from its accompanying strike group docked at a South Korean naval base in the southeastern port city of Busan on Tuesday.
The carrier was to conduct joint maritime exercises with South Korean forces on Monday off the Korean peninsula's south coast, South Korea's defence ministry said.
The carrier's planned visit, which marks the first since the USS Ronald Reagan visited in September, was arranged as part of efforts to have more US strategic assets in the area to deter North Korea, the ministry said.
Pyongyang said the missiles were aimed at tactical nuclear attacks and that the North Korean government has been ramping up its military tests in the past few weeks, including the firing of multiple cruise missiles on Wednesday.
On Friday, North Korea said it had tested a new nuclear-capable underwater attack drone, as leader Kim Jong Un warned that joint military drills by South Korea and the US should stop.
The allies concluded their regular springtime exercises, called Freedom Shield 23, last week, but have other field training continuing, including amphibious landing drills involving a US amphibious assault ship, and exercises with the US carrier.
Pyongyang has long bristled at the allies' drills, saying they are preparations for an invasion of the North.
South Korea and the United States say the exercises are defensive.