Iran has warned the United States that it would respond forcefully to any Israeli offensive on a mountainous ridge in southern Lebanon where Iranian military personnel are holed up alongside Hezbollah fighters, three officials briefed on the message told Reuters.

The message, delivered last month, highlights Iran’s continued direct involvement in the ground fighting in southern Lebanon and its readiness to retaliate against Israeli attacks there as the regional war enters its seventh month.

Defense Minister Israel Katz, meanwhile, said an Iranian attack on Israel would “free [the IDF] from all constraints,” and that in such a scenario, the military would “strike all infrastructure — including energy infrastructure — and return Iran to the Stone Age and darkness.”

Hezbollah, an Iranian proxy, is believed to have built an underground command center and weapons stores within the Ali Taher ridge, which has a commanding view of southeastern Lebanon, according to Lebanese security sources, and has become one of the most contested pieces of ground in the Israel-Hezbollah war.

According to the IDF, Hezbollah has a “strategic” underground facility beneath the hill, and that underground site is the “nerve center” of the terror group’s Badr regional division.