May later told reporters in her Downing Street office that the Western missiles struck a chemical weapons storage and production facility, a chemical weapons research centre and a military bunker involved in chemical weapons attacks.
U.K. Prime Minister Theresa May said the attack was "not about intervening in a civil war".
In a televised address, Trump said that the objective of the strikes was to "establish a strong deterrent" against the use of chemical weapons, and suggested that the strikes could continue beyond Friday, warning that the USA was ready to "sustain this response", if needed.
However, Kosachev said, the attack's meaning was clear: "It's a scandalous violation of global law and this is an attack on a sovereign state without an underlying basis".
"We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents", Trump said. The US responded by firing 59 Tomahawk missiles at a Syrian airbase that was suspected of playing a role in the chemical attacks. Hopefully, someday we'll get along with Russian Federation, and maybe even Iran - but maybe not.
Four Royal Air Force Tornado jets using Storm Shadow missiles had taken part in the attack on a military facility near Homs where it was assessed Syria had stockpiled chemicals, Britain's Ministry of Defence (MoD) said. She said the use of force was "right and legal" in this case.
US, UK and France launch air strikes on Syrian government targets
The action followed a week of threats of retaliation for an alleged chemical weapons attack on civilians in Douma, outside Damascus, where Syrian forces have always been battling rebels.
The Latest: A global chemical warfare watchdog group says its fact-finding mission to Syria will go ahead even after the US -led airstrikes. Another official said multiple types of bombs were used, and a variety of targets chosen.
He said it is hard to predict what the future holds.
According to the Russian Defense Ministry, Syria repelled the Western attack by air defense complexes made in the USSR over 30 years ago.
Russian President Vladimir Putin calls Macron on April 13 to warn against any "dangerous actions" with "unpredictable consequences", the Kremlin says. But the description from an ally described things differently.
France's defense minister, Florence Parly, tweeted a video of what she wrote was a naval cruise missile being launched from a French frigate in the Mediterranean.
At a Pentagon briefing, Mr Dunford said the latest air strikes were planned to minimize the risk of casualties among Russia's forces in Syria.
Coordinated airstrikes on targets associated with the Syrian regime's chemical weapons program have been carried out by a coalition of three nations.
The third target was a chemical weapons equipment storage facility and an important command post, also west of Homs, Dunford said.
May said there was "no practicable alternative" to the use of force against Assad.
East of Syria, the United States also has warships deployed in the Persian Gulf, and a significant presence at the Al Udeid airbase in Qatar.
Despite overwhelming evidence of the government's involvement in the attacks, Syria has denied responsibility for both incidents.
The decision to strike, after days of deliberations, marked Trump's second order to attack Syria.
"The U.S. Has no appetite for war", Hudson told News 4 Tucson's Eric Fink. Those bases come under the protection of Russian air defense units.
Syria's Soviet-made air defense systems have downed 71 out of 103 cruise missiles launched by the US and its allies, the ministry said.
The British Prime Minister insisted that military action against Bashar Assad's regime was a limited strike in response to the "harrowing" chemical weapons attack in Douma and was not about regime change. The commission, which is investigating the attack on Douma, is an independent body established by the UN Human Rights Council to investigate human rights violations in Syria.
Many waved Syrian, Russian and Iranian flags.
It was unclear if the strikes will deter Assad from again using chemical weapons.
In his nationwide address, Trump stressed that he has no interest in a longtime fight with Syria. "As other nations step up their contributions we look forward to the day we can bring our warriors home".