President Donald Trump warned the ceasefire in the Middle East war was on "life support" Monday after rejecting the latest counteroffer from Iran, which said its military stood ready to respond to any act of aggression.

The president's angry reaction to Iran's position -- delivered in response to a US proposal -- sent oil prices soaring and dashed hopes that a deal could be quickly negotiated to reopen the Strait of Hormuz to commercial shipping.

After slamming the reply as "TOTALLY UNACCEPTABLE," Trump insisted the United States would see a "complete victory" over Iran, adding that the truce which has largely halted fighting in the Gulf for over a month was on its last legs.

"The ceasefire is on massive life support, where the doctor walks in and says, 'Sir, your loved one has approximately a one percent chance of living,'" he told reporters on Monday.

Iranian parliamentary speaker Mohammad Bagher Ghalibaf, who served as chief negotiator in previous talks with Washington, said shortly afterwards that his country was prepared "for any eventuality."

"Our armed forces are ready to respond and to teach a lesson for any aggression," he wrote on X. "A bad strategy and bad decisions always lead to bad results -- the world already understands this."