North Korea has fired an unidentified projectile, South Korea's joint chiefs of staff said on Thursday, the second such launch within a week.
The launch came as the US envoy for North Korea is visiting the country, seeking an agreement on ending the rogue state's nuclear weapons proliferation programme.
On Saturday, the North carried out a military drill, firing at least one missile, believed to be a short-range weapon.
Thursday's projectile was fired at about 4:30pm local time (10:30 UTC+4) and it is not clear how many or what type of missile was launched.
"We are still analysing whether it is a single or multiple projectiles," Joint Chiefs of Staff spokesman Kim Joon-rak said, adding that the launch fired in an eastward direction appeared to originate from Sino-ri in North Pyongan province.
Sino-ri is a decades-old missile base, 75km of Pyongyang and is one of the country's longest-running facilities, hosting medium-range ballistic missiles.
The launch came hours after US Special Representative of North Korea Stephen Biegun arrived in Seoul for talks with their South Korean allies on a co-ordinated approach towards Pyongyang.
US and North Korean relations underwent a flurry of diplomacy last year when US President Donald Trump held a meeting with North Korean leader Kim Jong-un. Their second meeting in Vietnam this year, however, ended unceremoniously without a joint statement or even an agreement.
The Korean peninsula, which has been in a tense cold war for decades, underwent a rapid cooling of relations last year. But that has since slowed down and the leaders are struggling to find common ground.
Saturday's military drill rattled leaders in South Korea and the United States, prompting close analysis of the rogue state's movements.
The North said early on Thursday that Saturday's drill was routine, conducted in their own waters and did not pose a threat to the US, South Korea or Japan.
Analysts say that the missile was probably a Russian-imported missile.
"The debris generated by the launch in North Korea is a virtual match of a launch of Iskander conducted by Russia," 38 North, a website monitoring the situation in Korea, said.