The United States flew surveillance aircraft over the Korean Peninsula, an aviation tracker said, Monday, amid simmering tensions over possible provocative acts by North Korea after it warned of a "new strategic weapon."

An RC-135W Rivet Joint of the U.S. Air Force carried out operations over South Korea at 31,000 feet, Aircraft Spots tweeted.

This type of aircraft was last spotted over the peninsula last Wednesday, according to the aviation tracker. Several other surveillance aircraft, such as the EP-3E and the RC-135S, have conducted operations here often in recent weeks.

The latest flight comes amid growing concerns over provocative acts by the North ahead of the birthday of its leader Kim Jong-un that falls on Wednesday.

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Wrapping up a rare four-day party plenum last week, Pyongyang said it no longer feels bound by the self-imposed moratorium on nuclear and long-range missile tests, and warned that the world would witness a new strategic weapon "in the near future" amid stalled denuclearization talks with the U.S.

Experts say the North's "strategic weapon" may mean an intercontinental ballistic missile (ICBM) capable of carrying multiple warheads or a submarine-launched ballistic missile. (Yonhap)