"The escalation by the United States is unacceptable," Mohammad Javad Zarif said in Tokyo where he is holding talks with Japanese officials.

"We exercise maximum restraint... in spite of the fact that the United States withdrew from JCPOA last May," he added, referring to the nuclear deal known as the Joint Comprehensive Plan of Action.

He added that Tehran remains "committed" to the deal, and said continuing assessments showed Iran was in compliance with the multilateral agreement.

Tensions between the United States and Iran were already high after President Donald Trump withdrew from the nuclear deal a year ago.

But they have been ratcheted up significantly in recent weeks amid increased US pressure over alleged threats from Iran.

Earlier this month, Trump's hawkish National Security Advisor John Bolton announced the deployment of the USS Abraham Lincoln aircraft carrier strike group and a B-52 bomber force to the Gulf.

Days later, the Pentagon added a Patriot missile defence battery and an amphibious assault ship to the deployment.

And on Wednesday the US ordered the partial evacuation of its Baghdad embassy and consulate in Arbil citing specific threats posed by Iraqi militias alleged controlled by Tehran.