Syria's capital has been rocked by loud explosions that lit up the sky with heavy smoke as U.S. President Donald Trump announced air strikes in retaliation for the country's alleged use of chemical weapons.

Trump spoke from the White House Friday night. He said a "combined operation" with France and the United Kingdom is underway.

During a press conference with the Pentagon, Defense Secretary Jim Mattis said he is "absolutely confident" that Syrian President Bashar Assad is behind the alleged chemical attack on his people that the U.S. and allies retaliated against Friday night.

Mattis told reporters he is certain Assad conducted a chemical attack on innocent people.

He said the U.S. is "very much aware of one of the chemical agents used." And he said there may have been a second.

The president said that last Saturday, Syrian President Bashar Assad deployed chemical weapons in what was a "significant escalation in a pattern of chemical weapons use by that very terrible regime."

The British defense ministry said "initial indications" show that the air strikes against Syria produced a "successful attack" on a Syrian military facility.

The U.K. ministry said in a statement that while the effectiveness of the strike is still being analyzed, "initial indications are that the precision of the Storm Shadow weapons and meticulous target planning have resulted in a successful attack."

British Prime Minister Theresa May described the attack as neither "about intervening in a civil war" nor "about regime change," but a limited and targeted strike that "does not further escalate tensions in the region" and does everything possible to prevent civilian casualties.

May said, "We would have preferred an alternative path. But on this occasion there is none."

A highly placed Russian politician likened President Donald Trump to Adolf Hitler and said he regards the action as a move against Russia.

Alexander Sherin, deputy head of the State Duma's defense committee, said Trump "can be called Adolf Hitler No. 2 of our time — because, you see, he even chose the time that Hitler attacked the Soviet Union."

That's according to state news agency RIA-Novosti. The Nazi forces' opening attack against the USSR in 1941 was launched around 4 a.m.

Trump said America does not seek "an indefinite presence" in Syria and will look to pull out its troops once the Islamic State is totally defeated.

He has signaled in recent weeks that, despite advice from his national security team, he wanted to accelerate the timetable of the withdrawal of American forces.