BEIRUT — Issuing Tehran’s strongest warning to date, a top Iranian official said Saturday that any attack on Syria would be deemed an attack on Iran, a sign that it will do all it can to protect embattled Syrian President Bashar Assad.

Ali Akbar Velayati, an aide to Iran’s supreme leader Ayatollah Ali Khamenei, made his comments as Syrian troops conducted offensive air raids against rebels and discovered a trio of tunnels they were using to smuggle weapons in their fight to topple Assad.