A rocket was fired into Baghdad’s heavily-fortified Green Zone on Sunday, Iraqi military spokesperson Brigadier General Yahya Rasoul told AP. The Green Zone houses government buildings and foreign embassies.

The rocket landed near the Monument of the Unknown Soldier, which is about 500 metres north of the United States embassy compound. No group has claimed responsibility yet. Rasoul said the rocket is believed to have been fired from East Baghdad which is home to Iran-backed Shiite militias.

A US State Department official confirmed that a low-grade rocket landed in the Green Zone near the embassy, but no facility was impacted. “But, we take this incident very seriously,” an unidentified State Department official told Reuters. “We will hold Iran responsible if any such attacks are conducted by its proxy militia forces or elements of such forces, and will respond to Iran accordingly.”

Another unidentified US official said Washington may send additional personnel to protect the embassy. Hours after the blast, US President Donald Trump tweeted, “If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!”

This comes amid heightened tensions across the Persian Gulf. Earlier this month, the US had sent additional forces to the region to counter “credible threats from Iran”. Tehran had described the US move as “psychological warfare” and a “political game”. The US also has ordered all non-emergency government employees in Iraq to leave the country soon.

The Green Zone was regularly targeted during the US occupation of Iraq that ended in 2011. Since then, rockets have occasionally been fired into the zone. The latest was in September when three mortar shells landed inside the Green Zone.