Britain has backed the US missile strike on a Syrian air base as an "appropriate response" to Bashar Assad regime's "barbaric" chemical attack.
The Government has offered its full support to US president Donald Trump's targeted assault on the base from where he said a devastating nerve agent strike on civilians was launched.
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However, Russia has called the US missile strike on a Syrian airbase "aggression against a sovereign state in violation of international law".
President Vladimir Putin's spokesman, Dmitry Peskov, said Mr Putin believed the US had carried out the strikes under a "far-fetched pretext".
He said America had ignored previous incidents involving the use of chemical weapons by Syrian rebels, and that the Syrian government had destroyed such stockpiles under international control.
Earlier, the head of information policy commission in the upper house of the Russian parliament, Alexei Pushkov, tweeted that if Mr Trump launched military action in Syria it would put him in "the same league with Bush and Obama".
Vladimir Safronkov, Russian deputy envoy to the UN, said Russia had warned the US to "think about what military actions have led to in Iraq, Libya and other countries", according to Interfax news agency.
However, the US received support for the move from its allies, including Britain.
The surprise barrage of 59 cruise missiles in the early hours of Friday, UK time, was the first direct US attack on the Syrian government.
Mr Trump was reacting to the attack on Tuesday that killed at least 72 people, including 20 children, which he said was launched by Syrian president Assad.
On Friday morning, a No 10 spokeswoman said: "Overnight, the US has taken military action against the Syrian regime, targeting the airfield in Shayrut which was used to launch the chemical weapons attack earlier this week.
"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."
Speaking from Florida, Mr Trump announced his strike in an emotional message to the public in which he evoked images of children dying.
"Using a deadly nerve agent, Assad choked out the lives of helpless men, women and children. It was a slow and brutal death for so many," he said.
"Even beautiful babies were cruelly murdered in this very barbaric attack.
"Tonight, I ordered a targeted military strike on the airfield in Syria from where the chemical attack was launched.
"It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.
"There can be no dispute that Syria used banned chemical weapons."
US Tomahawk missiles, launched from two warships in the Mediterranean Sea, targeted airstrips, hangars, control towers and ammunition areas in Sharyat, central Syria, according to officials.
They suspect a mixture of chlorine and a nerve agent were used in Syria's attack on the largely opposition-held Idlib province.
Mr Trump said the latest action was in the "vital national security interest", adding that the US must "prevent and deter the spread and use of deadly chemical weapons".
He also called for other "civilised nations" to join efforts "seeking to end the slaughter and bloodshed in Syria".
Britain had been leading renewed calls for diplomatic action in response to the earlier chemical attack.
The US, UK and France had brought a resolution before the United Nations Security Council, demanding an investigation.
Earlier on Wednesday, Downing Street had played down the prospect of military action, insisting "nobody is talking" about an armed response to the atrocity.
Syrian state TV went on to report missile attacks on a number of military targets, calling them an act of "aggression" which had led to "losses".
Pentagon spokesman Captain Jeff Davis said the strike was a "proportional response to Assad's heinous act".
It succeeded in "reducing the Syrian government's ability to deliver chemical weapons" by severely damaging or destroying aircraft, according to initial indications, he added.
He also said Russian forces were alerted ahead of the strike to minimise casualties at the airfield.
US secretary of state Rex Tillerson said Russia had "failed" to deliver its commitment to secure Syria's chemical weapons, saying it had been either complicit or "simply incompetent".
Major Jamil al-Saleh, a Syrian opposition commander whose district has been hit by chemical weapons, welcomed the US attack and hopes it will be a "turning point" in the six-year civil war.
The Syrian Coalition opposition group also backed the move, with senior official Ahmad Ramadan urging Mr Trump to "hit the snake's head".
Australia's prime minister Malcolm Turnbull said his government "strongly supports the swift and just response of the United States".
"This was a calibrated, proportionate and targeted response," he said.
"It sends a strong message to the Assad regime and ... has been struck at the very airfield from which the chemical attack was delivered.
"But we are not at war with the Assad regime and the United States have made it clear that they are not seeking to overthrow the Assad regime."
Labour's Barnsley MP Dan Jarvis, a former paratrooper, said: "The use of chemical weapons constitutes a war crime for which the Assad regime must be held accountable
"The West's failure to act against this regime has served only to exacerbate the appalling suffering in Syria.
"Any strikes must be as precise as possible; between Assad and Isis the Syrian people have already endured far too much pain and loss."
Mr Jarvis went on to call for "a clear strategy for the country and region", adding: "Air strikes alone are never enough.
"They must be part of a plan to stabilise the country with negotiated no-fly zones, safe zones, and humanitarian extraction and supply routes all considered.
"If the air strikes are not part of a co-ordinated strategy, they run the risk of only furthering the suffering, either through the killing or injuring of civilians or the triggering of reprisals against them.
"President Trump must also understand that Russia remains critical to the stabilisation of Syria - it is not good enough to have two political strong men butting heads.
"Unless they find a stable solution, only the people of Syria will suffer."