Iran's Revolutionary Guards rejected a US proposal for a emergency line.
The same day Iran carried out strikes on US bases in Bahrain and Kuwait.
Both Kuwait and Bahrain confirmed the attacks.
US officials stated the strikes hit facilities used by American personnel.
The Iranian attack followed the hotline offer was made.
President Donald Trump warned that Iran's existence as a state won't survive.
He pledged additional military action against Tehran.
Trump said any any further aggression would be met with decisive force.
The rejection of the hotline and the fresh attacks heighten the risk of wider conflict.