North Korea has carried out an engine ignition test for a long-range missile capable of striking the western United States, a South Korean newspaper reported Tuesday.

A U.S. reconnaissance satellite detected the North testing the engine of what appears to be a Taepodong-2 missile — or an upgraded version of it — at a west coast missile base it began building several years ago, the mass-circulation Chosun Ilbo newspaper reported, quoting an unnamed South Korean government official.

The test took place earlier this year, the report said, without providing a date.

It would be a key step in development, and would confirm that the North has been working on a long-range missile. The entire missile base in North Pyongan Province in western North Korea is expected to be operational next year, the report said.

The Taepodong-2 missile can fly as far as 4,160 miles, and the upgraded version would take that range to more than 6,210 miles — within reach of the western United States.

South Korea's Defense Ministry said Tuesday it could not confirm the report because it involves intelligence affairs on North Korea.

Officials with the U.S. military command and U.S. Embassy in Seoul were not immediately available to confirm the report.

Construction of the North's new missile base is about 80 percent complete, South Korean Defense Minister Lee Sang-hee told a parliamentary committee last Thursday. He said the ministry is keeping a close eye on its construction.

Jane's Defence Weekly reported last week that the system is about one or two years from first-stage completion, but said the launch pad likely has had "emergency launch capability" since 2006.

North Korea's missile programs has been a key regional concern along with its nuclear weapons programs.

In 2006, the North conducted a series of missiles — including the Taepodong-2 — but experts said the Taepodong-2 missile plunged into the ocean shortly after liftoff.

Later in 2006, the North again rattled the world by conducting its first-ever test of a nuclear device. However, experts believe it does not have a bomb design advanced enough to be placed on a missile.