Iran summoned all European Union ambassadors Monday to protest the bloc’s listing of the paramilitary Revolutionary Guard as a terrorist group.

The move comes as Iran faces the threat of U.S. military action over its heavy-handed crackdown on recent mass protests. The American military has moved the USS Abraham Lincoln and several guided-missile destroyers into the Middle East.

However, it remains unclear whether President Donald Trump will decide to use force, though regional countries have engaged in diplomacy in an effort to halt a new Mideast war breaking out.

"Trump is trying to calibrate a response to Iran’s mass killing of protesters that punishes Iranian leaders without also embroiling the United States in a new, open-ended conflict in the region," the New York-based Soufan Center think tank said Monday.

"Some Trump aides seek to exploit Tehran’s weakness to secure major concessions from the regime, but Trump has set conditions for a diplomatic resolution that Tehran cannot accept."