The move was to send a message to Iran that although the US is not seeking war with Iran, but any attack on the US or its allies will be met with "unrelenting force". Recently, tension between the US and Iran is rising, as the US announced it will stop waivers for countries buying Iranian oil, in an attempt to reduce Iran's oil exports to zero.
It has also blacklisted Iran's elite Revolutionary Guard Corps. In response, Iran said it has mobilised all its resources to sell oil in a "grey market".
