Iran condemned airstrikes by the United States in Iraq and Syria as an act of "terrorism" on Monday, while denying any involvement in attacks against American forces in the region.

American fighter jets bombed five sites across Iraq and Syria on Sunday. They targeted weapons and munitions depots that U.S. officials said were linked to Iran-backed militias allegedly involved in violence against coalition bases in recent months.

At least 24 people were killed and 50 injured, according to local media quoting militia spokespeople.

Iraqi President Barham Saleh said the attack was "unacceptable and considered as an aggressive action and violation of Iraqi sovereignty."

The U.S. has about 5,000 troops in Iraq to train and assist government troops in the fight against the Islamic State militant group. In Iraq there are also a network of powerful militias, which are sanctioned by the state and many of which are backed by neighboring Iran.

On Sunday, American F-15s dropped precision-guided bombs on five sites in Iraq and neighboring Syria that the U.S. said were linked to some of these militias.

The U.S. said these militias were responsible for 11 rocket attacks against coalition bases in the last two months, including one that killed a U.S. contractor and injured four U.S. service members in Kirkuk on Friday morning.

Iran has denied that it's behind these attacks and on Monday denounced the U.S. airstrikes.

"We strongly condemn this aggression on Iraqi soil and say it's an example of terrorism," Foreign Ministry spokesman Abbas Mousavi said in a statement. "The U.S. has to respect the territorial integrity and independence of Iraq and to stop interfering in Iraqi internal affairs."

Mousavi also called on the U.S. to "end its occupation in the region."

U.S. Air Force F-15 fighter jets fly over Ukraine in October 2018. Gleb Garanich / Reuters

One of the militia groups targeted was Kataeb Hezbollah, also known as the Hezbollah Brigades in Iraq.

It is separate from the Lebanese militant group Hezbollah and operates under the umbrella of the state-sanctioned militias, known collectively as the Popular Mobilization Forces.

In a statement to its affiliated television station, Al Manar, Hezbollah condemned what it called "the brutal and treacherous American aggression."

According to Sanam Vakil, a senior research fellow at the London think tank Chatham House, the attacks and Tehran's response were evidence that Iran is trying to "push America's buttons."

"This simmering pot of water is now getting to a boil and we might start seeing more of these tit-for-tat escalations," she said. "Iran appears to be deliberately trying to provoke an American response. Why does it need that? To create a crisis to get back to the negotiating table."

In 2015, Washington joined other world powers in signing a deal that limited Iran's nuclear program in exchange for sanctions relief. In 2018, President Donald Trump, a longtime critic of the deal he described as weak, pulled the U.S. out of this accord.

"The U.S. president has repeatedly said he wants a deal and the Iranians have heard him," Vakil added. "But they have their own conditions for coming to the table: some sort of sanctions relief."

However, their ability to make progress is being squeezed by a number of factors including a lack of back-channels and domestic political tremors shaking both countries, she said.

"In the absence of all this, this is Tehran jumping up and down, trying to get some attention and provoke a crisis — even if that's a dangerous one that could lead to a serious overreaction at some point," Vakil said.

Speaking to reporters Sunday at President Donald Trump's Mar-a-Lago resort in Florida, Secretary of State Mike Pompeo said the airstrikes represented a "decisive response" to Iran.

"We will not stand for the Islamic Republic of Iran to take actions that put American men and women in jeopardy," he said.

The attack that killed the American contractor and U.S. counterstrikes come as months of political turmoil roil Iraq. About 500 people have died in anti-government protests, most of them demonstrators killed by Iraqi security forces.

The mass uprisings prompted the resignation last month of Prime Minister Adel Abdul-Mahdi, who remains in a caretaker capacity.

In a statement, Abdul-Mahdi said Secretary of Defense Mark Esper had called him about a half-hour before the U.S. strikes Sunday to tell him of U.S. intentions to hit the bases of the militia suspected of being behind Friday's rocket attack. Abdul-Mahdi said he asked Esper to call off the U.S. plan.

Ali Arouzi and Alexander Smith reported from London, and Charlene Gubash reported from Cairo.