The United States and South Korea have promised to keep up their guard and not reward bad behaviour by North Korea.
At a White House briefing with President Park Geun-hye on Tuesday, President Barack Obama said North Korea was more isolated than ever.
Ms Park is on her first foreign trip since taking office in February. Before their meeting, US officials said North Korea had moved two medium-range missiles from a coastal launch site, lowering tensions.
"The days when North Korea could create a crisis and elicit concessions, those days are over," Mr Obama said after meeting Ms Park in the Oval Office. He added:
"President Park and myself very much share the view that we are going to maintain a strong deterrent, we're not going to reward provocative behaviour, but we remain open to the prospect of North Korea taking a peaceful path.
"So far, at least, we haven't seen actions on the part of the North Koreans that would indicate they're prepared to move in a different direction," he said.
The United States and South Korea are marking 60 years of their military alliance.
Ms Park said her country would not tolerate North Korean aggression and escalation.
"Instead of just hoping to see North Korea change, the international community must consistently send the message with one voice, to tell them and communicate to them that they have no choice but to change,'' she said.
The BBC reports Pyongyang was believed to have been preparing for a missile launch last month, having threatened attacks in the region.
The threats followed new UN sanctions imposed on North Korea in March after a third nuclear test.
