Pyongyang tested an engine for its modernized long-range missile just a day before its third nuclear test on February 12, Yonhap news agency reported. Both of North Korea's missile launch sites are also being upgraded, Seoul has claimed.

An engine firing test for the KN-08 missile took place at the Dongchang-ri launch site in North Pyongan province last Monday, Yonhap reported. The new engine will extend the range of the KN-08 to 5,000 kilometers.

"If the North decides the test successful, it is expected to operationally deploy the new long-range rocket," an anonymous South Korean government source told Yonhap.

In March 2012, North Korea deployed six mobile ballistic missile complexes to celebrate the 100th birthday of Kim Il-sung, the founder of North Korea and grandfather of current leader Kim Jong-un, and showcased the arms in a military parade.

At the time, the US roundly criticized China for allegedly exporting the missile transporters to Pyongyang. The White House accused Beijing of delivering to North Korea in 2011 the “largest self-propelled overload special off-road transporter in China,” in defiance of a UN ban on such military sales; China denied the allegations.

The latest test-fire of the KN-08’s upgraded engine was carried out openly, Yonhap news agency’s source said, as North Koreans are well aware that their moves are being closely monitored by US spy satellites.

“The engine test right before its third nuclear test would be intended to intensify its threat to the US and its allies [South Korea and Japan],” Yonhap’s source explained.

North Korea's third nuclear test sparked immediate condemnation from the UN and the international community. Pyongyang reportedly responded by informing its primary ally China that it may stage two more nuclear tests before the end of this year.

A 100,000-person rally was held in Pyongyang to express support for the country’s leadership over the nuclear test.

The US, the first country that discovered that North Korea is modernizing its launch pads, accused Tehran of providing technical aid to North Korea.

“A new flame trench covering to protect large rockets from exhaust gases is similar to the covering used at a new launch pad at the Semnan Launch Complex in Iran,” explained the US-Korea Institute at Johns Hopkins School of Advanced International Studies in Baltimore, in a report dedicated to North Korea’s missile program.

The US-Korea Institute predicted that by 2016, North Korea may be able to build rockets with three to four times the range of the Unha-3 that Pyongyang tested in December, which successfully delivered the first North Korean satellite, Kwangmyongsong-3, into orbit.

“If North Korea continues to waste its budget on developing military weapons, it will become difficult to maintain its regime,” South Korean President Lee Myung-bak warned, according to Yonhap.

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