North Korea fired a suspected ballistic missile into the sea, a news report said, hours after the US and China announced they will work together to try to prevent North Korea from enhancing its nuclear weapons programme.
A projectile believed to be a ballistic missile flew into waters off the North's east coast, South Korea's Yonhap news agency reported, citing an unidentified military official.
South Korea's defence ministry said it could not immediately confirm the Yonhap report.
The launch, if confirmed, is the latest in a series of weapons launches the North has carried out in an apparent response to going military exercises between the US and South Korea. North Korea views the drills as an invasion rehearsal.
This year's drills, set to run until late April, are the biggest yet, and come after North Korea's nuclear test and long-range rocket test earlier this year.
President Barack Obama earlier met Chinese president Xi Jinping as world leaders gathered in the US capital for a nuclear security summit.
Both called for North Korea to give up its nuclear weapons, and China also agreed to implement in full the latest economic restrictions imposed by the UN Security Council against Pyongyang.
"Of great importance to both of us is North Korea's pursuit of nuclear weapons, which threatens the security and stability of the region," Mr Obama said at the start of his meeting with Mr Xi.
"President Xi and I are both committed to the denuclearisation of the Korean Peninsula."
Mr Xi said: "China and the US have a responsibility to work together."
As for their "disputes and disagreements," the Chinese leader said the two sides could "seek active solutions through dialogue and consultation".
More than 50 governments and international organisations are attending the two-day summit on preventing nuclear terrorism - the last in a series of global meetings Mr Obama has championed on the issue.
The risk posed by the Islamic State group tops this year's agenda but concerns about North Korea are also commanding focus.
Mr Obama also met Japanese prime minister Shinzo Abe and South Korean president Park Geun-hye. Together, they warned North Korea would face even tougher sanctions and more isolation if provokes again with nuclear and missile tests.
North Korea's fourth nuclear test in January, followed by a space a launch in February, have meant more agreement among the often-fractious powers in East Asia - at least on the need to press the government of Kim Jong Un towards disarming.
Japan and South Korea have persuasive reasons to get along. They both host US forces and are both in range of North Korean missiles.
But their relations have been plagued by historical differences that date back to Japan's colonial occupation of Korea in the first half of the 20th century and its military's use of sex slaves during the Second World War.
Those tensions have eased slightly, and Mr Abe said North Korea nuclear and missile capability is a "direct and grave threat" to them all.
"Should it choose to undertake yet another provocation, it is certain to find itself facing even tougher sanctions and isolation," Ms Park said of Pyongyang.
North Korea has also alienated its traditional benefactor and main trading partner, China.
The US has long urged Beijing to take a more forceful role in pressing North Korea, and Chinese vice foreign minister Zheng Zeguang said in Washington that the two sides agreed the new UN resolution "should be implemented in full and in its entirety".
On Tuesday, North Korea fired a short-range projectile that crashed into land in the North's north-east, according to South Korean defence officials.
The launch prompted media speculation in South Korea that Pyongyang may have tested a land target to test the accuracy of its weapons because the country has usually launched missile, artillery shells and rockets into the sea in the past.
Earlier this month, North Korea fired its first medium-launch missile into the sea since early 2014.