SEOUL, South Korea — North Korea has been conducting missile engine and fuel tests in recent weeks, with the goal of achieving nuclear-tipped intercontinental ballistic missile capabilities as early as next year, a senior South Korean official said on Tuesday.

Unification Minister Cho Myoung-gyon, South Korea’s lead official on North Korea, also said his government was closely monitoring missile-related activities in North Korea for a possible resumption of tests.

North Korea has not conducted a missile test since Sept. 15. The hiatus has raised cautious hopes in the region that the country might want to de-escalate after a series of missile and nuclear tests earlier this year and instead focus on bracing its economy for the pain expected to result from fresh sanctions.

But Mr. Cho said there could be other factors contributing to the lull in tests. He said North Korea had traditionally conducted fewer missile tests in winter. The country also needed time to clear key technical hurdles to achieving full-fledged intercontinental ballistic missile technologies, he said.