Russia and the United States have traded barbs at an ill-tempered emergency session of the UN Security Council called by Moscow after the US army launched a barrage of cruise missiles against a Syrian government airbase.

Syria's army said six people were killed in the early hours of Friday morning after the US fired nearly 60 Tomahawk missiles at Shayrat airbase, in retaliation for a suspected chemical weapons attack on a rebel-held town that killed scores of civilians earlier this week.

Vladimir Safronkov, Russia's deputy ambassador to the UN, "strongly" condemned the US for what he called a "flagrant violation of international law and an act of aggression".

"The consequences of this for regional and international stability could be extremely serious," he told the Security Council.

Russia is a key ally of Syrian President Bashar al-Assad, and has been bombing rebel-held areas in Syria since September 2015.

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For her part, US Ambassador Nikki Haley said the missile strikes were "fully justified" and warned that Washington was ready to take further military action.

"The United States took a very measured step last night," she told the council. "We are prepared to do more, but we hope it will not be necessary."

Mounzer Mounzer, deputy Syrian ambassador to the UN, called the US strike a "barbaric, flagrant act of aggression" that will embolden "terrorist groups" to use chemical weapons in the future.

According to the UK-based Syrian Observatory for Human Rights, at least 88 people, including 29 children, were killed in the suspected poison gas attack on Khan Sheikhoun in Idlib province, which the US has blamed on Assad.

Haley said the missile strikes destroyed the airfield from which the US believes Tuesday's suspected chemical attack was launched.

"The United States will no longer wait for Assad to use chemical weapons without any consequences," Haley said. "Those days are over."

While threatening further strikes, the US envoy also said it was time to press on with a political solution to the six-year war.

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Marwan Bishara, Al Jazeera's senior political analyst, questioned whether the missile barrage was simply bravado, or part of a larger strategic plan.

"Is it because US President Donald Trump wants to prove he is a resolute, decisive leader who is independent of [Russian President Vladimir] Putin, or is this punitive attack part of a comprehensive effort aimed at leveraging American influence in Syria to lead to a diplomatic solution," he said.

Haley also took a swipe at Russia for failing to rein in its ally, and said Moscow must reconsider its support for Assad.

"The world is waiting for the Russian government to act responsibly in Syria. The world is waiting for Russia to reconsider its misplaced alliance with Bashar al-Assad," she said.

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The US said 58 of the 59 cruise missiles fired at the Shayrat airfield hit their targets, dealing heavy damage to the base.

But the Russian defence ministry downplayed the damage, claiming only 23 missiles landed on target.

Satellite footage showed many of the runways were fully intact, as well as several untouched defence surface-to-air rocket launcher and radar systems.

Less than 24 hours after the US strike, two Syrian jets took off from the targeted base and bombed nearby rebel targets, according to the Observatory, which monitors Syria's conflict via a network of contacts on the ground.

Regardless of its damage, the attack - Trump's biggest military decision since taking office - marked a dramatic escalation in US involvement in Syria's war.

It followed days of outrage over images of dead children and victims suffering convulsions from the suspected poison gas attack in Khan Sheikhoun.

After the strike, Russia's defence ministry notified the Pentagon it would suspend its communication with US forces in Syria, while Dmitry Medvedev, the Russian prime minister, told on social media that the strikes had brought the US "one step away from military clashes with Russia".

US jets frequently attack Islamic State of Iraq and the Levant (ISIL) fighters in Syria and come close to Russian forces.

US officials informed Russian forces ahead of the missile strikes, and avoided hitting Russian personnel.

The Syrian government and Moscow have denied that Syrian forces were behind the gas attack, but Western countries have dismissed their explanation that chemicals leaked from a rebel weapons depot after an air strike as not credible.

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US allies from Asia, Europe and the Middle East expressed support, if sometimes cautiously, for Friday's missile barrage.

Opposition figures hailed the move as "first good steps" but demanded they be included within a larger strategy aimed at ending the war.

Homs Governor Talal Barazi said the US' direct strike on the Syrian military was a clear sign it was supporting "terrorists".

The action is likely to be interpreted as a signal to Russia, as well as countries such as North Korea, China and Iran - where Trump has faced foreign policy tests early in his presidency - that he is willing to use force.