Washington, June 23 (IANS): North Korea has tested a new rocket engine as part of its efforts to build a missile capable of reaching the American mainland, US officials said.

The officials told Fox News that the latest engine test on Thursday was conducted in the city of Yun Song, where previous rocket tests have taken place.

It could be one stage of an intercontinental ballistic missile (ICBM) engine that would be able to reach the US, the officials said.

The news of another rocket engine test by Pyongyang comes as an US official said on Wednesday there were signs of increased activity at North Korea's lone nuclear test site. 

North Korea has conducted five nuclear tests since 2006, including two last year, the report said.

Since hosting China's President Xi Jinping at his Mar-a-Lago Club in April, President Trump hoped China would help de-escalate tensions in the region following a series of ballistic missile tests, the report said.

"While I greatly appreciate the efforts of President Xi and China to help with North Korea, it has not worked out. At least I know China tried!" Trump said in a tweet earlier this week.

Tensions between the US and North Korea spiked once again last week when American student Otto Warmbier, who was serving a hard labour sentence in Pyongyang for allegedly stealing a propaganda sign, died shortly after returning home in a coma.

The US has also ramped up its military presence in the region, conducting drills with Japan as well as South Korea, and is installing a controversial missile defence system in Seoul, known as Terminal High-Altitude Area Defence system (Thaad).

But South Korea had suspending the further deployment of the system until an environmental assessment was completed.