North Korea has fired another missile into the Yellow Sea after sending a chilling warning to the US.
Citing South Korean military officials, local media reported that "at least one" short-range ballistic missile was fired towards the sea, which lies between the Korean peninsula and mainland China.
It comes after Kim Jong-Un's sister threatened to make the "Pacific our firing range" after it launched two short-range ballistic missiles towards Japan at the end of February.
The move drew quick condemnation from the country's rivals and prompted Tokyo to request an emergency meeting of the United Nations Security Council.
The firings follow an intercontinental ballistic missile (ICBM) launch and North Korea's threats to take an unprecedentedly strong response to US-South Korean military drills that the North views as an invasion rehearsal.
Some experts say North Korea is pushing for more powerful weapons that it believes would increase leverage in potential negotiations with the United States.
Kim Jo-yong, the powerful sister of leader Kim Jong-un, said Pyongyang would fire into the ocean depending on the actions of the US.
She said: "The frequency of using the Pacific as our firing range depends upon the US forces' action character."
"We are well aware of the movement of US forces' strategic strike means, (which are) recently getting brisk around the Korean Peninsula.
She could be referring to the US flyover of B-1B long-range, supersonic bombers for separate training with South Korea and Japan.
North Korea is extremely sensitive to the deployment of B-1B bombers, which can carry a huge payload of conventional weapons.
South Korea's military said it detected the two missile launches on Monday morning from a western coastal town just north of Pyongyang, the North Korean capital.
Kim Yo-Jong has been the mouthpiece used to make several threats against the West in recent weeks. On March 7, she said Pyongyang was ready to take "quick, overwhelming action against the US and South Korea.
Her combative comments came the same day the US flew a nuclear-capable B-52 bomber in the region.
The US-South Korean training on Monday involving the B-52 bomber over the Korean Peninsula was the latest in a series of drills between the allies in recent months.
Their militaries are also preparing to revive their largest field exercises later this month.
Kim Yo-jong did not describe any planned actions in her statement but North Korea has often test-launched missiles in response to US-South Korean military drills because it views them as an invasion rehearsal.
"We keep our eye on the restless military moves by the US forces and the South Korean puppet military and are always on standby to take appropriate, quick and overwhelming action at any time according to our judgment," Ms Kim said in the statement carried by state media.
