It’s not clear which regional country he is talking about here.

“Based on certain intelligence, Iran’s enemies, with the backing of a regional country, are preparing an operation to occupy one of Iran’s islands. All enemy movements are under the full surveillance of our armed forces. If they take a single step, all vital infrastructure of that regional country will be targeted without restriction in relentless strikes.”

The context strongly points to the UAE as they have a dispute with Iran over Abu Musa, Greater Tunb, and Lesser Tunb, which Iran has controlled since 1971.

Other possibilities are Bahrain or Saudi Arabia.