North Korea's ICBM engine test last week showed that the communist nation could make its road-mobile long-range missiles deliver nuclear warheads as far as the U.S. east coast, including Washington and New York, a U.S. expert warned Monday.

The North claimed Saturday that it successfully conducted a ground "jet test of a new type high-power engine" of an intercontinental ballistic missile, with leader Kim Jong-un saying that the test "provided a firm guarantee for mounting another form of nuclear attack upon the U.S. imperialists."

On Monday, John Schilling, an expert on North Korean missile capabilities, said the test involved "a tightly-coupled pair of propulsion units from an old Soviet submarine-launched ballistic missile," known as R-27 or SS-N-6, a technology that gives a missile greater range than Pyongyang's traditional mix of kerosene and nitric acid.

"Using this technology, North Korea's road-mobile intercontinental ballistic missile (ICBM), the KN-08 or the KN-14 modification, could deliver a nuclear warhead to targets at a distance of 10,000 to 13,000 km," the expert said in an article carried by the 38 North website.

"That range, greater than had previously been expected, could allow Pyongyang to reach targets on the US east coast, including New York or Washington, DC," he said.

Schilling also said that if the current ground test program continues and is successful, flight tests of a North Korean ICBM could "begin in as little as a year" and Pyongyang may be able to deploy this delivery system in a limited operational capability by 2020.

"North Korea's April 9 test of a large liquid-fuel engine is a disturbing development that not only highlights the growing threat posed by Pyongyang but should also put to rest, once and for all, all claims that the North's WMD programs are a hoax," he said.

"In fact, the test demonstrated that North Korea has an even greater capability at a more advanced state of development than previously anticipated," he added. (Yonhap)