Donald Trump said North Korea has “gotta behave” as tensions between the two countries have become increasingly strained.
Mr Trump made the remark while speaking during festivities at the annual White House Easter egg roll.
In the past, Mr Trump has taken to Twitter to say North Korea was "behaving very badly" and "playing" with the US.
North Korea unveiled new missiles during a large military parade in Pyongyang to celebrate the 105th anniversary of founding leader Kim Il-sung.
The spectacle was followed by a test of their so-called intercontinental missile, which failed just five seconds after launch, observers in the US and South Korea said.
US battleships were moved into the waters near the Korean peninsula as a precaution.
Mr Trump’s warning came just hours after Vice President Mike Pence made an unscheduled stop during his Asia tour to visit the Demilitarised Zone (DMZ) between North and South Korea.
The stop was part of Mr Pence’s Asia tour. “The era of strategic patience is over,” Mr Pence said.
He added that the US wants to see “North Korea abandon its reckless path of the development of nuclear weapons, and also its continual use and testing of ballistic missiles is unacceptable.”
Dr Bruce Bennett, Senior International Defense Researcher at Rand Corporation, told The Independent that Mr Trump’s comment “will not be taken well in Pyongyang.”
“For Kim Jong-un to “behave” along the lines the US demands would violate the North Korean culture — it would appear that Kim would be acting weak,” said Mr Bennett.
He said Mr Jong-un would likely want to demonstrate his power by testing another nuclear weapon or missile as a result.
“Such a test, of course, would force the South Korean people to think that Kim is more dangerous than they normally believe,” Mr Bennett explained.
He also said the situtation is made more complicated due to a change in the South Korean presidency about to take place after Park Geun-hye has had to resign from office due to political scandal.
Secretary of State Rex Tillerson also visited the border area in March 2017 and said that pre-emptive US military action was “on the table”.