President Donald Trump on Thursday ordered missile strikes against a Syrian airfield, where a deadly chemical weapons attack was launched days before.

Trump ordered the military action a day after denouncing Syrian President Bashar al-Assad for the poison gas attack, which killed at least 70 people, many of them children, in the Syrian town of Khan Sheikhoun. 

The strike is the toughest direct action the United States has taken in Syria’s six-year-old civil war.

"It is in the vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons," Trump said from his resort in Mar-a-Lago Thursday night.

On Saturday, an air strike believed to have been carried out by the U.S.-led coalition against Islamic State killed 15 people including four children in a village west of the jihadists' stronghold of Raqqa on Saturday, the Syrian Observatory for Human Rights said.

Here’s what you should know about the attack:

Where and when were the missiles launched?

More than 50 Tomahawk missiles were launched from the USS Porter and USS Ross, which are in the eastern Mediterranean Sea. The strike was conducted at 8:45 p.m. The target was the Shayrat Air Base, controlled by Assad's forces, and is where the chemical attack on Tuesday was launched from.

How many people died and what was the damage to the base?

The Syrian army said the U.S. attack killed six people at its airbase. Russian television said nine aircrafts had been destroyed and showed craters and rubble at the site of the airbase.

What was Syria’s response?

The Syrian army called the attack "blatant aggression" and said it made the United States a "partner" of "terrorist groups" including ISIS. 

Assad's office said Damascus would respond by striking its enemies harder: "This aggression has increased Syria's resolve to hit those terrorist agents, to continue to crush them, and to raise the pace of action to that end wherever they are."

What was Russia’s response?

The military action put Trump at odds with Russia, which has air and ground forces in Syria. The country had intervened in Syria on Assad's side in 2015.

Russian President Vladimir Putin condemned the strikes, calling them illegal. 

"President Putin views the U.S. strikes on Syria as aggression against a sovereign state in violation of the norms of international law and on a made-up up pretext," a Kremlin statement said. "This step by Washington will inflict major damage on U.S.-Russia ties."

Russia was informed of the strike before it happened.

Will there be more attacks on Syria?

The United States has been conducting air strikes against ISIS, but had avoided direct confrontation with Assad until now. 

U.S. officials said the attack was a one-off that would not lead to wider escalation, and Secretary of State Rex Tillerson said the strike did not mean the wider U.S. policy on Syria had changed.

U.S. lawmakers from both parties said they supported Trump's decision to order the strike and urged him to lay out a broader strategy for dealing with the ongoing conflict.

Does Trump support ousting Assad?

Trump said earlier on Thursday that "something should happen" with Assad but did not specifically call for his ouster. 

U.S. Ambassador to the United Nations Nikki Haley had said days before that the U.S. diplomatic policy on Syria was no longer focused on making Assad leave power, one of former President Barack Obama's aims. But Trump said on Wednesday the gas attack had caused him to think again about Assad.

A reversal for Trump

The deployment of military force against Assad marked a major reversal for Trump.

When Obama threatened military action after a 2013 chemical attack, Trump issued a series of tweets opposing the idea, including “Do NOT attack Syria, fix U.S.A.”

Obama backtracked on the air strikes, and after the latest attack, Trump was quick to blame his Democratic predecessor for “weakness and irresolution” that emboldened Assad.