North Korea is on notice as US President Donald Trump warns strategic patience is "over".
Mr Trump met with his South Korean counterpart Moon Jae-in at the White House, where the pair spoke about a lack of progress against Pyongyang.
"The era of strategic patience with the North Korean regime has failed. Frankly, that patience is over," he said while standing alongside Mr Moon in the White House Rose Garden.
"We are facing the threat of the reckless and brutal regime in North Korea. The nuclear and ballistic missile programmes of that regime require a determined response.
"We're working closely with South Korea and Japan, as well as partners around the world, on a range of diplomatic, security and economic measures to protect our allies and our own citizens from this menace known as North Korea."
President Moon has also warned that threats from the North will be met with a stern response.
The US President also took aim at Seoul over trade and the need for burden sharing in defence.
Mr Trump said at the start of his second day of talks with Mr Moon that the United States was renegotiating what had been a "rough" trade deal with South Korea.
"We will do more to remove barriers to reciprocal trade and market access," he said, adding that the two leaders had talked about the thorny trade areas of steel and cars.