Russia and Iran condemned a US strike on a Syrian airbase on Friday as Australia, Britain and Turkey gave their support, with Australian Prime Minister Malcolm Turnbull calling it a "proportionate" response to the use of chemical weapons.
US President Donald Trump ordered missile strikes against a Syrian airfield from which a deadly chemical weapons attack was launched, declaring he acted in America's "vital national security interest".
In a sharp escalation of the US military role in Syria, two US warships fired dozens of cruise missiles from the eastern Mediterranean Sea at the airbase controlled by President Basha Assad's forces in response to the poison gas attack in a rebel-held area on Tuesday, US officials said.
Russian President Vladimir Putin believes the strikes broke international law and seriously damaged US-Russia relations, news agencies cited the Kremlin as saying on Friday.
Iran denounced the "destructive and dangerous" strike, the Students News Agency ISNA quoted a Foreign Ministry spokesman as saying.
"Iran strongly condemns any such unilateral strikes ... Such measures will strengthen terrorists in Syria ... and will complicate the situation in Syria and the region," ISNA quoted Bahram Qasemi as saying.
Britain gave its backing.
"The UK government fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime and is intended to deter further attacks," a government spokesman said.
Turnbull said the strikes sent "a vitally important message" that the world would not tolerate the use of chemical weapons.
"The retribution has been proportionate and it has been swift," he told reporters in Sydney. "We support the United States in that swift action."
Turnbull said the military action was not designed to overthrow the Assad regime, although the reported use of chemical weapons did "raise questions as to whether there can be any role for Mr. Assad in any solution or settlement".
Turnbull called on Russia to do more to ensure peace in Syria.
Turkey viewed the strikes positively and the international community should sustain its stance against the "barbarity" of the Syrian government, Deputy Prime Minister Numan Kurtulmus said.
In an interview with Turkish broadcaster Fox TV, Kurtulmus said Assad's government must be fully punished in the international arena and the peace process in Syria needed to be accelerated.
French Foreign Minister Jean-Marc Ayrault said Russia and Iran needed to understand that supporting Assad made no sense and that the escalation of the US military role in Syria was a "warning" to "a criminal regime".
"Use of chemical weapons is appalling and should be punished because it is a war crime," Ayrault told Reuters and France Info radio in the Mauritanian capital, Nouakchott, where he is on a diplomatic visit.
Indonesia, home to the world's largest Muslim population, said it also strongly condemned the use of chemical weapons in Syria.
"At the same time, Indonesia is concerned with unilateral actions by any parties, including the use of Tomahawk missiles, in responding to the chemical weapon attack tragedy in Syria," Foreign Ministry spokesman Armanatha Nasir said in a text message.
"Military actions, undertaken without prior authorisation of the UN Security Council, are not in line with international legal principles in the peaceful settlement of disputes, as stipulated in the UN Charter."
A spokesman for the Polish government said the United States was a guarantor of world peace and there were times when you needed to react.