Beirut - The firing of a barrage of US cruise missiles at a Syrian airbase on Friday in response to a suspected chemical attack, has drawn furious condemnation from the Damascus regime and its key ally Russia.
US allies rallied around Washington after President Donald Trump launched the massive strike in retaliation for the "barbaric" chemical attack he blamed on the government of his counterpart Bashar Assad.
But Assad's office called the strike "foolish and irresponsible" and Moscow announced a series of retaliatory steps including plans to strengthen Syrian air defences.
The strike - the first direct US action against Assad's government and Trump's biggest military decision since taking office - marked a dramatic escalation in American involvement in Syria's six-year civil war.
It followed days of outrage at images of dead children and victims suffering convulsions from the suspected sarin gas attack in the rebel-held town of Khan Sheikhun.
US officials said 59 Tomahawk cruise missiles were fired from Navy ships in the Mediterranean at the Shayrat airfield at 03:40 (00:40 GMT), dealing heavy damage to the base from where Washington believes Tuesday's deadly attack was launched.
Syrian state news agency SANA said nine civilians, including four children, were killed in villages near the base.
"What America did is nothing but foolish and irresponsible behaviour, which only reveals its short-sightedness and political and military blindness to reality," Assad's office said in a statement.
Syria's regime has denied using chemical weapons in Khan Sheikhun, where at least 86 people, including 30 children, were reported killed and more than 500 wounded.
With US Secretary of State Rex Tillerson due in Moscow next week, the Kremlin called the US strike a "gross... violation of international law" and warned it would inflict "considerable damage" on US-Russia ties.
It demanded an emergency meeting of the UN Security Council and immediately suspended a deal with the United States aimed at avoiding clashes in Syrian airspace.
The Russian military also announced a series of measures "to strengthen and improve the effectiveness of the Syrian armed forces' air defence system" in the wake of the strike.
Foreign Minister Mohammad Javad Zarif of Iran, another staunch Assad ally, said on Twitter that the US strike was based on "bogus CW (chemical weapons) allegations" and would aid jihadists in Syria like the Islamic State group.
Britain, France, Germany, Israel, Japan, Saudi Arabia and Turkey all supported Washington, with Ankara also calling for a no-fly zone in Syria.
Trump announced the strike in a brief televised address delivered hours after the UN Security Council failed to agree on a probe into the suspected chemical attack.
"Tonight I call on all civilised nations to join us in seeking to end this slaughter and bloodshed in Syria and also to end terrorism of all kinds and all types," Trump said.
The missiles were fired from the USS Porter and the USS Ross, which belong to the US Navy's Sixth Fleet, in the eastern Mediterranean.
The strike targeted radars, aircraft, air defence systems and other logistical components at the base south of Homs in central Syria.
US officials said measures had been put in place to avoid hitting sarin gas they said was stored at the airfield.
In a statement read on state television, the Syrian army confirmed the strike and said it had caused extensive damage.
The Russian military said the strike had an "extremely low" military impact, with fewer than half of the 59 missiles reaching the base.
The strike destroyed six planes under repair and several buildings, including a storage depot and radio station, it said.
Syria's opposition and rebel fighters, who have for years urged more direct US military action in support of their uprising, hailed the strike and called for more.
The National Coalition, the main opposition grouping, called on Washington to take further steps to "neutralise" the regime's air power.
"We hope for more strikes... and that these are just the beginning," spokesperson Ahmad Ramadan told AFP.
Syria's rebels have suffered a series of setbacks in recent years as Assad's forces have reclaimed much of the territory once under opposition control.
The White House was quick to paint the decision as limited to deterring the use of chemical weapons, and not part of a broader military campaign.
"The intent was to deter the regime from doing this again, and it is certainly our hope that this has had that effect," Pentagon spokesman Navy Captain Jeff Davis told reporters.
US officials said Russia's military in Syria was informed of the strike beforehand in order to avoid casualties that could prompt a broader crisis.
Russia stood by Damascus this week despite the global uproar, insisting that the chemical weapons that caused the deaths in Khan Sheikhun had been stockpiled by "terrorists" and possibly released by a conventional strike.
Tillerson accused Russia of being incompetent or complicit in permitting Assad's actions and said Friday's strike should leave no one in any doubt that Trump is willing to act if any actor "crosses the line".
Trump had previously indicated no willingness to engage further in Syria's civil war, beyond stepping up efforts to battle the jihadists of ISIS, who have been targeted by US-led air strikes in Syria and Iraq since mid-2014.
His administration had in fact signalled in recent days that it was no longer seeking the Syrian leader's departure from power.
But Trump said the "very barbaric attack" in which "even beautiful babies were cruelly murdered" had required a response.
Analysts said the US strike did not necessarily reflect a shift in policy on Assad.
"It seems unlikely that these events change the overall US calculus towards the regime," said Tim Eaton, a research fellow with the Middle East and North Africa programme at think tank Chatham House.
"The US administration still has significant reservations about the Syrian opposition," he said. "It seems to me that removing that one airfield does not shift the balance of power in terms of the conflict."