An escalating war of words has broken out between Moscow and Washington over a suspected chemical attack in a Syrian rebel-held town, raising international tensions amid calls for action at an urgent UN Security Council meeting.

The US, Britain, France and six other countries requested Monday’s emergency session after rescue teams and medics said a “poisonous chlorine gas attack” in Douma on Saturday killed dozens of people, including many children and women.

The Syrian government of President Bashar al-Assad and its ally Russia have called the allegations “fabrications”.

As the fallout continued on Monday, Nikki Haley, the US ambassador to the UN, told the urgent meeting that Washington was ready to “respond” to the attack regardless of Security Council acted or not.

“We have reached the moment when the world must see justice done,” Haley said, striking a sombre and threatening tone.

“History will record this as the moment when the Security Council either discharged its duty or demonstrated its utter and complete failure to protect the people of Syria,” she added. “Either way, the United States will respond.”

Moments earlier, Vassily Nebenzia, Haley’s counterpart, had called the chemical attack allegations “fake news” and said Russia was ready to fly weapons’ inspectors to the site to see for themselves.

Warning that any military action against Syria’s government could have “grave repercussions”, the Russian ambassador also accused US, France and Britain of “hawkish rhetoric” and “boorishness against my country”, adding that their lack of a clear strategy for Syria was “appalling”.

‘Abrasive rhetoric’

Al Jazeera’s Mike Hanna, reporting from the UN headquarters in New York, said the he different narratives and the “escalation in rhetoric” laid bare the divide within the Security Council.

“The statement from the Russian ambassador was as abrasive as has been heard within the Security Council for a long period of time,” he said.

“The responses from the US and its allies were equally stern and gloomy, so certainly there is a level of debate within the council that is possibly more abrasive, more confrontational and less constructive than we’ve heard before.”

Meanwhile, Staffan de Mistura, the UN envoy to Syria, issued an urgent call for unity and action at the emergency meeting.

“I urge the Security Council, in accordance with its own mandate, to maintain international peace and security and uphold international law to, for God’s sake, ensure a mechanism is found to investigate this allegation and attribute responsibilities.”

Earlier on Monday, US President Donald Trump pledged to soon announce “major decisions” over the attack, while his  Russian counterpart, Vladimir Putin, warned against “provocation”.

In a statement, the Kremlin said Putin had held a phone conversation with German Chancellor Angela Merkel, during which the two “leaders exchanged opinions on the situation in Syria, including the accusations against Damascus by a number of Western countries of using chemical weapons.

“The Russian side stressed the unacceptability of provocation and speculation on this matter,” the Kremlin added.

For his part, Trump condemned what he called a “heinous attack on innocent” Syrians in Douma, as he opened a cabinet meeting at the White House, adding that decisions would come in the “next 24-48 hours”.

Trump and French President Emmanuel Macron have also vowed a “strong, joint response”, while Jim Mattis, the US defence secretary, said nothing was off the table in terms of military action.

In April last year, Trump ordered air raids on Syrian government facilities in the wake of a chemical attack in  Khan Sheikhoun , a rebel-held town, which killed at least 80 people.

“The question now is whether the president will have a similar reaction after seeing similar images coming out of Douma,” Al Jazeera’s Kimberly Halkett, reporting from Washington, DC, said, adding that several emergency meetings with military and political advisers were taking place in and around the White House on the matter.

On Sunday, Trump warned Iran and Russia that there would be a “big price to pay” for backing the “animal Assad”.

Meanwhile Theresa May, the British prime minister, said on Monday that the Syrian government “and its backers, including Russia, must be held to account” if it is found to be responsible for dropping chemical weapons on Douma residents.

But Kremlin spokesperson Dmitry Peskov warned that “making any deductions is wrong and dangerous”, suggesting that rebels could have staged the attack themselves to pin the blame on Damascus.

Sergey Lavrov, Russia’s foreign minister, said Russian specialists had found no trace of a chemical attack on Douma.

The heated exchange of remarks also came after missiles struck a Syrian airbase  in Homs province earlier on Monday, state media reported, with Russia and Syria blaming Israel for carrying out the attack.

Two Israeli fighter jets, using Lebanese airspace, fired eight missiles at the T-4 military airbase, the Russian military said, but offered no further information.

The attack at the airbase, located 40km west of Palmyra, killed and wounded several people, Syrian state news agency SANA reported, citing an unnamed military source.

Israel has not responded to the accusations.