Theresa May has hinted the UK would be prepared to take part in military action against the regime of Bashar al-Assad following the apparent use of chemical weapons in Syria.

The prime minister said “initial reports” suggested the attack, in which at least 42 people were killed, was another example of the “brutality” of the Syrian regime.

Asked if she was considering direct British military action in response, May told a press conference in Copenhagen the UK and its allies were discussing “what action is necessary”.

“We are very clear, if this is a chemical weapon attack of the sort it appears to be from the regime, we want to to ensure those responsible are held to account,” she said.

And in a challenge to Russia, May said the supporters of the Assad government “must be held to account too”.

May said Russia’s repeated use of its veto at the UN has “enabled” international rules on chemical weapons attacks to be broken and investigations hampered, May said. “This must stop,” she added.

US President Donald Trump described al-Assad as an “animal” after the attack, and warned there would be a “big price to pay”.

Israel has been accused by Moscow of launching a retaliatory attack on a Syrian government airbase, which hit near Homs on Sunday.

Russia’s Foreign Minister Sergei Lavrov describing the strike as a “provocation” and a “very dangerous development”. 

Observers say at least 14 people were killed in the retaliatory strike on the Syrian T-4 air base.

Israel, which has previously hit Syrian targets, has not commented.

Speaking on Monday morning, Downing Street confirmed the UK played no role in the military action.

The prime minister’s spokesman said: “The reports of a chemical weapons attack are deeply disturbing and its vital that they must be urgently investigated and the international community must respond.

“We are swiftly working with our allies to agree a common position.

“We are one of the countries which called for the emergency security council meeting which will take place later today.”

The spokesman said any investigation must be “resolved as swiftly as possible”, and added: “We would also make the point that Russia must not yet again try to obstruct these investigations.”

Downing Street explained the UK believes Russia tried to “obstruct” investigations into previous chemical weapons attacks in Syria.

Jeremy Corbyn, avoided blaming Assad when asked if he believed the Syrian leader was behind the chemical attack.

Speaking at the launch of Labour’s local election campaign in London, Corbyn said “evidence” needed to be gathered to determine “exactly who delivered that chemical weapon”.

“On the chemical attack, I condemn it absolutely. I condemn the use of chemical or biological weapons in any scenario anywhere in the world,” the Labour leader added.

“The UN has called for an urgent and rapid inquiry into it and indeed the re-opening of inquiries into previous uses of chemical weapons. The tragedy and the terror of people’s lives in Syria can only end by a political solution.”

Corbyn said every country in the region, as well as Russia and the US should come together “to ensure there is a meaningful cease-fire and a political process to bring about a solution to the terror and the tragedy and the conflict that has wasted so many lives in Syria.”

The Syrian government has denied its forces had launched any chemical assault, while Russia at the weekend called the reports fake and warned against military action on the basis of “invented and fabricated excuses”.

The UN Security Council will meet twice on Monday following rival requests by Russia and the United States to discuss the incident, and the Organisation for the Prohibition of Chemical Weapons chief, Ahmet Uzumcu, has “expressed his grave concern in response to the alleged chemical weapons attack on 7 April in Douma.”

US government sources said Washington’s assessment of the Saturday attack was that chemical weapons were used. The European Union also said evidence pointed to the use of chemical weapons by Assad’s forces.

A European diplomat said Western allies would work on building a dossier based on photos, videos, witness testimony and satellite images of Syrian flights and helicopters. However gaining access to samples on the ground would be difficult.

UN war crimes investigators had previously documented 33 chemical attacks in Syria, attributing 27 to the Assad government, which has repeatedly denied using the weapons. 

On Monday the French President Emmanuel Macron spoke to Trump by telephone and the two agreed they would work together to establish clear responsibility for the chemical attack, which Macron’s office said they had agreed to confirm.

Macron said in February “France will strike” in the event of lethal chemical weapon attack on civilians by government forces in Syria. A French defence ministry official said on Monday France did not carry out the air strike on the T-4 base.

The medical relief organisation Syrian American Medical Society (SAMS) and the civil defence service, which operates in rebel-held areas, said in a joint statement that at least 42 people had been killed in the suspected gas attack.

One video shared by activists showed bodies of about a dozen children, women and men, some with foam at the mouth. “Douma city, April 7 … there is a strong smell here,” a voice can be heard saying. Reuters could not independently verify the reports.

Last year the United States launched a cruise missile strike on a Syrian air base in response to the killing of dozens of civilians in a sarin gas attack in an opposition-held town in northwest Syria. The gas attack was blamed on Assad.