BEIJING, Jan. 1 (Xinhua) -- Hundreds of protesters on Tuesday stormed the U.S. embassy in Baghdad, mourning for the Hashd Shaabi members killed by a U.S. attack in Iraq on Sunday, which has prompted the United States to send additional troops to the Middle East.

"Approximately 750 soldiers will deploy to the region immediately and additional forces from the IRF (the Immediate Response Force) are prepared to deploy over the next several days," said Secretary of Defense Mark Esper.

"This deployment is an appropriate and precautionary action taken in response to increased threat levels against U.S. personnel and facilities, such as we witnessed in Baghdad today," Esper added.

Many of the protesters, wearing Hashd Shaabi military uniforms, rallied outside the embassy chanting slogans condemning U.S. airstrikes. The protest then turned violent as protesters set ablaze a guard tower and the outer gate of the embassy.

Hashd Shaabi, an Iraqi state-sponsored umbrella organization formed by Iraq's Shi'ite-led paramilitary Kata'ib Hezbollah (KH), said on Monday that U.S. drones bombarded its military bases near Iraq's border with Syria, which killed 25 people and wounded 51 others.

The attack came two days after a rocket barrage hit a U.S. military camp, killing a U.S. contractor and wounding others, which the United States blamed on the KH, a militia allegedly backed by Iran, the long-time foe of the United States. Both are the most influential players in the region.

U.S. President Donald Trump said in a tweet on Tuesday that "Iran killed an American contractor, wounding many. We strongly responded, and always will. Now Iran is orchestrating an attack," which "they will be held fully responsible (for)."

Iraq on Monday condemned the U.S. attack, saying it was "a violation of Iraq's sovereignty" in a statement by the Iraqi National Security Council, and denied any role in the recent deadly attacks on the U.S. forces.

"This unsubstantiated U.S. claim cannot justify the bombing and killing of people in violation of international regulations," Iranian government spokesman Ali Rabiee said.

Rabiee said that the U.S. attack was another proof of its "destructive" role in the region, particularly in Iraq, and it once again showed that "as long as the U.S. keeps its uncalled-for presence in Iraq and Syria, peace will be unattainable for all."