U.S. President Donald Trump said Thursday he ordered a missile strike on an airfield in Syria from which a chemical attack using a deadly nerve agent was allegedly launched earlier this week, killing dozens of civilians including children.

The airstrike was in the United States' "vital national security interest to prevent and deter the spread and use of deadly chemical weapons," Trump said, referring to Washington's direct intervention in Syria in retaliation to Tuesday's suspected chemical attack in a northern city held by the rebels.

The U.S. Defense Department said 59 Tomahawk land attack missiles were fired from two destroyers in the Mediterranean Sea and targeted the base's aircraft, petroleum and logistical storage, air defense systems, radars and other facilities.

"There can be no dispute that Syria used banned chemical weapons," Trump told reporters at his Mar-a-Lago retreat in Palm Beach, Florida. Calling Syrian President Bashar al-Assad a "dictator," he accused the regime for violating obligations under the Chemical Weapons Convention by using a deadly nerve agent against innocent civilians.

It is the first U.S. military action against Assad's regime since Syria's civil war starting in 2011 and reflects Trump's change in position to take a tougher stance against the Syrian leader. Washington's unilateral action came amid a lack of progress in U.N. Security Council measures in dealing with the civil war.

Trump denounced the attack on civilians, including babies, as "barbaric" and called on "all civilized nations" to join the United States to end the "slaughter and bloodshed" in Syria and also to end all forms of terrorism.

"Years of previous attempts at changing Assad's behavior have all failed, and failed very dramatically," said Trump. He said that as a result, the refugee crisis deepens and regional destabilization in the region continues, "threatening the United States and its allies."

Syrian state television reported that the U.S. missile attack on the country's air base had "no legitimate grounds," while a military source of Assad's regime said there was damage in the base attack.

According to Reuters, the rebels, the Syrian national coalition opposition group, said they welcome the attack.

Reuters also quoted a Pentagon official as saying the attack is a one-time action, and the United States has no plans to launch further attacks.

The U.S. missiles hit at 3:45 a.m. Friday local time the Shayrat air base in central Syria, from which U.S. officials say the Syrian military planes that unleashed Tuesday's chemical attack had taken off.

Pentagon spokesman Capt. Jeff Davis said in a statement that the air base was "used to store chemical weapons" and that the strike aims to "deter the regime from using chemical weapons again."

Davis said initial indications show the strike reduced the Syrian government's ability to deliver chemical weapons.

He also revealed that the U.S. military gave Russia advance notice of its strike and was careful not to hit areas of the base where Russian personnel are located. Moscow has continued to back Assad's regime.

Meanwhile, in Florida, where Trump is in for a two-day summit with Chinese President Xi Jinping, U.S. Secretary of State Rex Tillerson said that "steps are underway," when asked if he and Trump will be organizing a global coalition to remove Assad from power.

The U.S. government believes the man-made nerve agent sarin was used in the attack. The odorless and colorless nerve gas, which can be absorbed through the skin, is considered one of the most toxic chemical warfare agents.

The incident, if confirmed, would be the deadliest chemical attack in Syria since sarin gas killed several hundreds of people in a rebel-held area near Damascus in August 2013. Western states believe the Syrian government was responsible for that attack as well.