WASHINGTON - For the first time since the beginning of Syria's civil war, the United States on Thursday bombed an Assad regime military base in response to the chemical weapons attack launched on Syrian citizens earlier this week.

According to a Pentagon spokesperson, 59 Tomahawk missiles were fired at Shayrat airbase outside of Homs, Syria, the site from which the U.S. suspects the chemical attack originated. Targets included "aircraft, hardened aircraft shelters, petroleum and logistical storage areas, ammunition supply bunkers, air defense systems and radars."

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Open gallery view An image of the Shayrat airfield in Syria released by the U.S. Department of Defense, October 7, 2016. Credit: HANDOUT/REUTERS

Syria called the operation "an aggression" while state TV reported nine civilians killed. Rebels welcomed the U.S. operation.

U.S. President Donald Trump said after his meeting with Chinese President Xi Jinping that the airstrikes were a national security interest of the United States. He called on "the civilized nations of the world" to join the U.S. in "ending the slaughter and bloodshed in Syria."

Trump also said that years of attempting to change Assad's behavior have failed. and that the Syrian leader's actions and the resulting refugee crisis have created risks for the United States and its allies.

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The U.S. military gave Russian forces advanced notice of its strikes and did not hit sections of the base where the Russians were believed to be present, Pentagon spokesman Captain Jeff Davis has said.

Davis, briefing reporters on the operation, said the U.S. military had "multiple" conversations with Russian forces on Thursday before the strike, using a line of communication that had previously been established to prevent an accidental clash in Syria during the fight against Islamic State.

The Pentagon noted that "extraordinary measures" were taken to prevent Russian casualties.

The Lebanese TV station al-Mayadeen reported that the Syrian army command had evacuated most warplanes from an air base before it was struck. In a news flash, al-Mayadeen said its report was based on "information."

A Syrian state news agency said that the U.S. missile attack killed nine civilians, including four children, in areas near the base. The Syrian army reported extensive damage, adding that it would respond by continuing its campaign to "crush terrorism" and restore peace and security to all of Syria.

A statement from the army command described the attack as an act of "blatant aggression," saying it had made the United States "a partner" of Islamic State, the Nusra Front and other "terrorist organisations."

Open gallery view U.S. President Donald Trump addressing the U.S. airstrikes in Syria, April 7, 2017. Credit: JIM WATSON/AFP

Russian President Vladimir Putin called the strikes an "aggression against a sovereign nation" which violated international law. Saying the attack was carried out on an "invented pretext," a Kremlin spokesman added that the strikes do significant damage to U.S.-Russian relations.

Russia also said it is suspending its agreement to communicate with the U.S. on the use of Syrian airspace.

The spokesman added that no Russians were hurt in the attack.

Russia also backed Syria's claim that its army is not in possession of any chemical weapons.

The Israeli Prime Minister's Office released a statement praising the strikes, saying President Trump sent a strong message that the use and distribution of chemical weapons won't be tolerated.

The Prime Minister's Office added that Israel hopes Trump's powerful message against the Assad regime will be heard not only in Damascus, but also in Tehran and Pyongyang.

A senior Israeli official said that Israel was among the countries notified by the Pentagon before the strikes.

Syrian opposition group, the Syrian Coalition, welcomed the U.S. attack, saying it puts an end to an age of "impunity" and should be just the beginning.

Major Jamil al-Saleh, a U.S-backed rebel commander whose Hama district in the country's center was struck by the suspected chemical weapons attack, told AP he hoped the U.S. attack would be a "turning point" in the war that has left more than 400,000 dead.

The governor of Syria's Homs province, meanwhile, said that the strikes serve the goals of "armed terrorist groups" and ISIS. "Syrian leadership and Syrian policy will not change," Homs governor Talal Barazi said in a phone interview with state television. "This targeting was not the first and I don't believe it will be the last," he added.

He added that rescue teams and firefighters were continuing their efforts inside the base and the sites that were hit.

Saudi Arabia said it "fully supports" the U.S. strikes on Syria, calling it a "courageous decision" by Trump in response to the use of chemical weapons against civilians.

"A responsible source at the foreign ministry expressed the Kingdom of Saudi Arabia's full support for the American military operations on military targets in Syria, which came as a response to the Syrian regime's use of chemical weapons against innocent civilians...," a statement carried by state news agency SPA said.

U.S. Secretary of State Rex Tillerson said that the U.S. has a high degree of confidence that sarin nerve gas was used in the Idlib attack. He said that Russia has failed to carry our the 2013 agreement to secure Syrian chemical weapons, adding that Moscow was either complicit or incompetent in its ability to carry out the agreement.

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Republican Senators Lindsey Graham of South Carolina and John McCain of Arizona, who in recent days both criticized Trump after his administration announced that it did no longer consider Assad's ouster as a strategic goal, put out a statement on Thursday night praising the president for the airstrikes. "Unlike the previous administration, President Trump confronted a pivotal moment in Syria and took action," it said.

New York Democrat and Senate Minority Leader Chuck Schumer also backed Trump. "Making sure Assad knows that when he commits such despicable atrocities he will pay a price, is the right thing to do." Schumer added that "it is incumbent on the Trump administration to come up with a strategy and consult with Congress before implementing it."

Rep. Ed Royce, a California Republican and the head of the House of Representatives' Foreign Relations Committee, said in response to the strike: "Assad was warned repeatedly by the United States that the intentional targeting of innocent men, women and children is intolerable. Now Assad has been caught red-handed carrying out another abhorrent chemical attack and the administration has taken a measured response."

Reuters and AP contributed to this report.