North Korea said on Sunday that it carried out the test successfully at its Sohae Satellite Launching Ground, referring to its Dongchang-ri site in North Pyongyan province, the previous day, reports Yonhap News Agency.
Pyongyang did not elaborate on what it tested but noted that results "will have an important effect on changing the strategic position of North Korea once again in the near future".
Choi Hyun-soo, South Korean Defence Ministry spokesman, said: "We are aware of North Korea's announcement. In close coordination with the US, we keep close tabs on moves in major sites in North Korea, including the Dongchang-ri site."
She, however, stopped short before giving out details of the test's initial assessment.
According to satellite imagery analyzed on Monday by Planet Labs, an American imaging company, North Korea could have carried out a missile engine test at the Dongchang-ri site, Efe news reported.
The images detected activity around the vertical engine test and appeared to show indications of altercations to the surface that could have been caused due to high temperatures of the engine exhaust.
In the past, North Korea has used the site to test rocket engines and launch vehicles to deliver satellites, and such technology could be diverted to develop and launch long-range weapons.
In March 2017, North Korea successfully tested a new high-thrust engine at the station, which was employed to launch Inter Continental Ballistic Missiles (ICBM), such as the Hwasong-14 and Hwasong-15, later that year.
In June 2018 after his summit with North Korean leader Kim Jong-un, US President Donald Trump said that the former had promised to dismantle the Donghang-ri site.
During his summit with South Korean President Moon Jae-in in September 2018 in Pyongyang, Kim made the same pledge, said Yonhap News Agency.
The test came as Pyongyang has ramped up pressure on the US to meet its demand for a new negotiating proposal by the year end, strongly suggesting that otherwise, it could restart testing of nuclear weapons and ICBM.
The North last conducted a nuclear test in September 2017 and an ICBM test in December 2017, though it recently carried out a series of short-term ballistic missile and projectile firings.
Last week, the North reiterated that the deadline was drawing closer, saying that it was "entirely" up to the US what "Christmas gift" it wants to get, putting pressure on Washington to take first action in making concessions.
( With inputs from IANS )