On Tuesday, U.S. officials revealed that North Korea tested another advanced ballistic missile engine last Friday. It was the third such test in the past month.

The precise nature of this engine was not revealed in CNN’s report, which quoted American officials uncertain the engine could be used in an ICBM. Previous tests have raised concerns that North Korea is getting close to producing a reasonably accurate missile that could hit the continental United States.

An American official pointed out to Fox News that none of the three rocket engines “ended in an embarrassing explosion,” which is an unpleasant indication that North Korea is making progress in its designs.

Fox News notes that recent surveillance indicates the movement of a missile launcher and construction of VIP seating in Wonsan, suggesting a new high-profile missile launch is imminent.

Other satellite imagery of North Korea’s primary nuclear test site shows vehicles and trailers moving around, water being pumped from a test tunnel, and the deployment of fresh communications cables, indicating that another nuclear bomb test could occur soon.

Reuters notes, however, that analysts have not yet seen definitive evidence of a nuclear device moving to the site and that North Korea is not above faking an imminent nuclear test, fully aware that satellites are watching their every move.

April 15th is the birthday of North Korean founder Kim Il-sung, grandfather of current dictator Kim Jong-un. The anniversary is seen as a likely moment for Kim to stage another bomb and/or missile test.

The Australian reported on Monday that Australian Foreign Minister Julie Bishop was told by the commander of U.S. and U.N. forces in South Korea that North Korea is very close to nuclear strike capability against her country. Bishop said it was the first time she has heard a warning about Pyongyang’s threat to Australia in “such stark terms.”

Japan grows increasingly nervous as well. The governing Japanese Democratic Party has been actively campaigning to develop pre-emptive strike capabilities against North Korea, a campaign grown more urgent after Pyongyang’s recent launch of four test missiles at Japan.

“Japan can’t just wait until it’s destroyed. It’s legally possible for Japan to strike an enemy base that’s launching a missile at us, but we don’t have the equipment or capability,” said Japanese Democratic Party head Hiroshi Amazu.

In a sign of how seriously American and regional defense planners take the North Korean situation, both F-35B Marine warplanes and a nuclear-powered fast-attack submarine, the USS Columbus, have been added to joint military exercises with South Korea.