Iran's supreme leader, Ayatollah Ali Khamenei, warned on Sunday that any "inappropriate action" over US claims of a Tehran-directed assassination plot would be met with a "decisive response."
"If American officials are entertaining any illusions, they should know that any inappropriate action -- whether political or security-related -- will meet the Iranian people's decisive response," he said in a speech in western Iran, according to his official website.
The remark came as US officials consult with allies and other countries on the possibility of ratcheting up economic pressure on Iran, which is already subject to UN and US sanctions over its controversial nuclear programme.
Iran has fiercely denied any involvement in the thwarted plot to assassinate the Saudi ambassador to Washington.
But US President Barack Obama has vowed Iran will "pay a price" for what he says is incontrovertible proof it had a hand in trying to contract a Mexican drug cartel to carry out the hit.