North Korea has launched a series of short-range missiles into the sea off its east coast, according to the US military, while South Korea and the Americans have been carrying out joint military drills.
Tensions between North Korea and the US flared up earlier this month after US President Donald Trump said he would unleash "fire and fury" on Pyongyang if it made any escalation against the Americans.
A war of words then broke out between Trump and North Korea as negotiators worked behind the scenes to calm the conflict.
North Korea threatened the US by saying that it was preparing a plan to strike Guam, a US army base in the Pacific.
Global stock markets were rocked amid fears of a war breaking out between the two sides.
Now, the US military Pacific Command has said North Korea has fired three short-range ballistic missiles over a 20 minute period, just days after American officials praised North Korean leader Kim Jong Un for not undertaking any missile tests since July.
The missiles used would not have the ability to strike Guam, the US said.