North Korea has carried out another test of a rocket engine that the United States believes could be part of its program to develop an intercontinental ballistic missile, a U.S. official told Reuters on Thursday.

The United States assessed that the test, the latest in a series of engine and missile tests this year, could be for the smallest stage of an ICBM rocket engine, the official said, speaking on condition of anonymity.

A second U.S. official also confirmed the test but did not provide additional details on the type of rocket component that was being tested or whether it fit into the ICBM program.

One official said he believed the test had taken place within the past 24 hours.

The disclosure of the engine test came a day after the United States pressed China to exert more economic and diplomatic pressure on North Korea to help rein in its nuclear and missile programs during a round of high-level talks in Washington.

U.S. President Donald Trump has warned that a “major, major conflict” with North Korea is possible over its weapons programs, although U.S. officials say tougher sanctions, not military force, are the preferred option.

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