TEHRAN, April 6 (Xinhua) -- At least 13 people were killed early Monday after an airstrike hit a residential building in Eslamshahr, a city south of Tehran, the Fars news agency and Nour News reported.

It was not immediately clear why the building was targeted. Neither Israel nor the United States claimed responsibility for the strike.

The strike came hours after U.S. President Donald Trump threatened to unleash "hell" on Iran if the Strait of Hormuz is not reopened.