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The United States has launched 59 Tomahawk cruise missiles against Syrian government targets in retaliation for what the Trump administration charges was a Syrian government chemical weapons attack that killed scores of civilians, the Pentagon says.

The US strikes hit the government-controlled Shayrat air base in the central province of Homs, where US officials say the Syrian military planes that dropped the chemicals had taken off.

The strikes were the first direct military action the US has taken against Syrian President Bashar al-Assad's forces in the six-year war. 

The US missiles hit at 3:45am Friday morning in Syria and targeted the base's airstrips, hangars, control tower and ammunition areas, officials said.

Trump called on "civilised nations" to join US in "seeking to end the slaughter and bloodshed in Syria".

"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," he said.

Syrian state TV said "American aggression targets Syrian military targets with a number of missiles".

READ MORE: Survivors of the Idlib attack share their stories

The US warned Russia, which carries out air strikes in Syria, ahead of the raid, the Pentagon said.

"Russian forces were notified in advance of the strike using the established deconfliction line," Navy Captain Jeff Davis said, referring to a special military hotline.

"US military planners took precautions to minimise risk to Russian or Syrian personnel located at the airfield."

Separately, Secretary of State Rex Tillerson said "We sought no approval from Moscow".

Earlier on Thursday, Russia's deputy ambassador to the UN warned of "negative consequences" if the United States took military action against Syria. 

"First of all we have to think about negative consequences," Vladimir Soronkov told reporters in response to
questions about possible US strikes.

"All responsibility if military action occurred, will be on shoulders of those who initiated such doubtful and tragic enterprise."

The US military said initial indications were that the strikes had severely damaged or destroyed Syrian aircraft and support infrastructure and equipment at the airfield.

The suspected poison gas attack on the rebel-held town of Khan Sheikhoun in Idlib province on Tuesday killed at least 86 people, including 27 children, according to the UK-based Syrian Observatory for Human Rights. 

Turkey said samples from victims of the attack indicate they were exposed to sarin, a highly toxic nerve agent.

"I think what happened in Syria is a disgrace to humanity and he [President Bashar al-Assad] is there, and I guess he's running things, so something should happen," Trump had told reporters earlier on Thursday.

Christopher Swift, professor of national security studies at Georgetown University, said the most important question was whether the Trump administration's vision in launching the strikes was "an impulsive one or a strategic one".

"It's not clear to me, yet, whether this administration has thought through the implications of the actions they took this evening," he told Al Jazeera.

"If the president has a plan, then it will be interesting to see how that plan comes through. But if he doesn't, he may have done more harm than good."

At the time of the US raid, Trump was at his Mar-a-Lago estate in Palm Beach, Florida, where he is holding two days of meetings with Chinese President Xi Jinping.

Trump said the strike on Syria was in the "vital national security interest" of the United States.

Al Jazeera's James Bays, reporting Palm Beach, said: "This may be a one-off operation but it will be quite difficult now for Trump to get himself out of the argument over the future of Syria, the political future of Assad, the UN talks process in Geneva - the Trump administration is now at the centre of it all."

Syria maintains it did not use chemical weapons, blaming opposition fighters for stockpiling the chemicals.

Russia's defense ministry said the toxic agents were released when a Syrian air strike hit a rebel chemical weapons arsenal and munitions factory on the eastern outskirts of Khan Sheikhoun.

"I stress, once again, that the Syrian Arab Army did not and will not use such weapons even against the terrorists who are targeting our people," Syria's Foreign Minister Walid al-Muallem told reporters in Damascus.

Idlib hospitals overwhelmed after suspected gas attack

Source: Al Jazeera and news agencies