Barack Obama has pledged to work with China to prevent North Korea from developing nuclear weapons
North Korea is reported to have fired a missile into the sea just hours after South Korea, Japan and the United States warned Pyongyang to end its provocations.
The surface-to-air missile was fired from a region close to the North's eastern coast, according to a South Korean military official.
Yonhap news agency reported it flew a distance of around 100km.
Tensions have heightened on the Pyongyang-Seoul border since the North's nuclear test in January and long-range rocket launch in February.
Friday's drill is the fourth missile launch by Kim Jong-Un's regime in recent weeks - and the second in four days - amid military exercises involving South Korea and the US, the largest ever carried out by the two nations.
It comes as President Barack Obama, his South Korean counterpart Park Geun-hye and Japanese Prime Minister Shinzo Abe agreed to pressure the secretive state over its nuclear programme.
The three leaders met on the sidelines of a global nuclear summit in Washington aimed at reducing the risk caused by the proliferation of nuclear technology.
Mr Obama said: "We are united in our efforts to deter and defend against North Korean provocations. We have to work together to meet this challenge."
Mr Obama also held separate talks with President Xi Jinping of China, the closest North Korea has to an ally,
Both said they wanted to see "full implementation" of the latest United Nations sanctions against Pyongyang.
Existing UN sanctions ban North Korea from conducting any ballistic missile test.
At a news conference with Mr Obama, Mr Xi said that while Washington and Beijing disagreed in some areas, they have had "effective communication and co-ordination".
The meetings took place on the fringes of the Nuclear Security Summit at which leaders of more than 50 countries discussed securing vulnerable atomic materials to prevent nuclear terrorism.
Seven years after Mr Obama hosted the first Nuclear Security Summit, he reiterated the need to enforce UN security measures.
Russia, which together with the US possesses more than 90% of the world's nuclear arsenal, said it would skip the event because of a "shortage of mutual cooperation" on the agenda.
Pakistan also announced it would not be attending.
According to the Stockholm International Peace Research Institute, the US has 7,700 nuclear weapons and Russia 8,000.