North Korean leader Kim Jong Un on Tuesday called for an increase in his country's nuclear arsenal, saying it should be fully prepared to use it at any time, the North's KCNA news agency reported, as a US aircraft carrier nears reaching South Korea.
This comes after South Korea's military said Pyongyang had fired two ballistic missiles into the sea off its east coast on Monday.
The South Korean military also condemned the launch, calling it a "serious provocation" in violation of United Nations Security Council resolutions, and called for an immediate halt to the operations.
The Japanese government also lodged a "strong protest" with North Korea, saying its missile launches threatened the safety and security of Japan, the region and the international community.
The USS Nimitz and its escort ships are scheduled to dock at a South Korean naval base in the southeast of the country.
South Korea's defense ministry said the planned visit to the aircraft carrier was arranged as part of efforts to deploy more U.S. "strategic military assets" to the region to deter North Korea.
North Korea has stepped up military tests in recent weeks, including several cruise missile launches on Wednesday, in a test Pyongyang said was intended to train for tactical nuclear attacks.