A North Korea-related website run by a U.S. think tank said Pyongyang conducted an unannounced test of a liquid-propellant rocket engine at the Sohae Satellite Launching Station late last month.

The Center for Strategic and International Studies'(CSIS) Beyond Parallel website, citing analysis of satellite imagery from April 29 and other sources, said the North carried out the test at Sohae station's Yunsong vertical engine test facility during the fourth week of April.

CSIS assessed that the unannounced test is a clear indication that the regime is continuing to pursue the development of liquid-propellant rocket engine technology for both its ballistic missile and space launch vehicle(SLV) programs.

It is unknown if North Korean leader Kim Jong-un was present to observe the latest test.

In early April, several sources indicated to CSIS that North Korea was preparing to conduct its second military reconnaissance satellite launch, following the launch of the Malligyong-1 satellite last November.