The United States fired cruise missiles at Syria last night in response to this week's chemical attack that killed more than 80 Syrian civilians — the first direct U.S. assault on the Bashar al-Assad government and Donald Trump's most dramatic military order since becoming president.

The strikes hit the government-controlled Shayrat airbase in central Syria. U.S. officials say the airbase was the originating point for the military planes behind Tuesday's gas attack, said to have involved the use of chlorine mixed with a nerve agent, possibly sarin.

The UN held an emergency meeting on the situation.

59 missiles launched

Fifty-nine Tomahawk missiles were launched from the USS Ross and USS Porter in the Mediterranean Sea, with 58 of them hitting their intended targets in Syria at 3:45 a.m. local time Friday. The missiles targeted the base's airstrips, hangars, control tower and ammunition areas, U.S. officials said.

A U.S. official said all but one of the missiles struck their intended targets.

Trump ordered the strike from his Mar-A-Lago resort in Florida, where he is hosting Chinese President Xi Jinping.

Assad "launched a horrible chemical weapons attack on innocent civilians using a deadly nerve agent," Trump said in a prepared statement after the cruise missile attack became public knowledge.

Shayrat military airbase

The airstrike in Syria targeted the Shayrat military airbase in Homs. (CBC)

"There can be no dispute that Syria used banned chemical weapons, violated its obligations under the chemical weapons convention and ignored the urging of the UN Security Council," Trump said, calling it a "targeted" strike.

The Syrian military said at least seven people were killed and nine wounded in the missile strike. The Britain-based Syrian Observatory for Human Rights, an opposition monitor, also put the death toll at seven, including a general and three soldiers. 

Cellphone video captures U.S. missile strikes in Syria0:44

A statement from the army command described the attack as an act of "blatant aggression," saying it had made the United States "a partner" to the likes of the Islamic State of Iraq and Syria and other militant groups.

Syria said the strike would not deter it from driving out those groups.

'Act of aggression,' says Russia

The Kremlin early Friday confirmed it received advance warning, while a Russian lawmaker was quoted by Interfax as saying no Russians were injured, according to his sources.

Russian officials said six jets were destroyed. The head of the Syrian Observatory for Human Rights said over a dozen hangars and a fuel depot were also damaged. 

A Kremlin spokesperson said Russian President Vladimir Putin sees the missile strikes as an act of "aggression against a sovereign state in violation of international law." Iran issued a similar statement.

Russia said it would now suspend a deal with the U.S. to prevent mid-air incidents over Syria, and that it would help Syria strengthen its air defences again. ​

Trump US China

Cruise missiles were launched at Syria around the time Trump and Chinese President Xi Jinping sat down for a dinner in Palm Beach, Fla., at the beginning of a two-day summit on April 6, 2017. (Alex Brandon/The Associated Press)

U.S.-Russia hotline still open

Senior U.S. military officials say Russia has agreed to maintain a hotline aimed at preventing midair collisions in Syria.

The declarations contradict Russia's claim that it has suspended military "deconfliction" talks after the American missile strikes.

The officials say there have been U.S.-Russian discussions since Thursday night's attack of the Syrian military base. They say American officials have sought to make sure the talks would continue, and the Russians have provided confirmation they will.

The officials weren't authorized to speak publicly on the matter and demanded anonymity.

The hotline was established after Russia intervened militarily in 2015 to ensure Russian and U.S. planes conducting combat missions in Syria's skies don't stumble into an accident or confrontation.

Could complicate quagmire

It's unclear what authority Trump is relying on to attack another country. When Obama intervened in Libya in 2011, he used a UN Security Council mandate and NATO's overall leadership of the mission to argue that he had legal authority — arguments that many Republicans opposed. Trump can't rely on either justification here.

Donald Trump on airstrikes against Syria2:50

In Syria, the Obama administration largely pulled back from its support for so-called "moderate" rebels when Russia's military intervention in September 2015 led them to suffer a series of battlefield defeats. Instead, Obama sought to work with Russia on a negotiated transition.

Trump called on "civilized nations" to join U.S. now but it's unclear whether he is adopting any broader effort to combat Assad.

The assault risks plunging America into the middle of Syria's conflict, complicating the safety of the hundreds of U.S. forces fighting a separate campaign against the Islamic State group in the north of the country.

With files from Reuters and CBC News