President Trump's Defence Secretary says a Syria strike could cause the conflict to spiral out of control.
President Macron also said they will decide whether to strike back when all the necessary information has been gathered from Syria.
The chemical weapons watchdog has released its findings on the poisoning of an ex-Russian spy and his daughter in Salisbury, UK.
Euronews speaks to experts about the alleged chemical attack in Douma that activists say killed dozens and wounded hundreds more.
Vladimir Chizov says the events purported to be a chemical attack in Syria's Eastern Ghouta region were staged
The NGO also calls for more aid to be allowed in to worst hit areas of Syria
Save the Children calls for inspectors to verify if chemical weapons were used in deadly attack in Damascus' eastern suburb.
Several people have died in what Syrian state TV claims was a US missile attack on a major air base in the country. Washington has denied the claims.
At least 70 people including children are known to have died in the attack on the rebel-held town of Douma near the capital Damascus
At least 70 dead after suspected gas attack in Syria. The reports cannot be independently verified and the Syrian government rejects the allegations.
Meanwhile, Russia's Ambassador to the EU Vladimir Chizhov appeared to backtrack on previous suggestions that the nerve agent used in the UK attack could have come from a British laboratory.
A ceremony has been held in memory of the 5,000 people who died
Secretary general Stoltenberg says, "it's important that we react in a proportional, measured and defensive way".
It is an assault on the UK 's sovereignty and any such use by a state party is a clear violation of the Chemical Weapons Convention and a breach of international law, the powers say.
Britain had hoped for a different scenario but it's now heading into a major showdown with Russia, a senior official at the Royal United Services Institute (RUSI) think tank tells Euronews.
New Scotland Yard has given a statement on the latest in its investigation into the Russian spy poison attack in Salisbury.
Below is a transcript of a statement by British prime minister Theresa May to parliament on the subject of Russian involvement in a chemical attack on two people in the town of Salisbury.
Theresa May convened her National Security Council on Monday and was due to address parliament later in the afternoon to discuss how to respond to the attempted murder of former Russian spy Sergei Skripal.
UK Foreign Minister Boris Johnson vows to give a 'robust response' to the attack on former Russian spy Sergei Skripal and his daughter Yulia.
Russia wants a new independent investigation but the US wants to press ahead with prosecuting the Assad regime. Meanwhile chemical attacks are reportedly ongoing.
The international community is sending a dangerous message to despots, dictators and terrorists the world over: stamping out chemical warfare is not a priority, writes Hamish de Bretton-Gordon
Russia has rejected a United Nations Security Council resolution to investigate alleged chemical weapons attacks in Syria.
The US-backed draft
The report blames the Assad regime for a chemical strike that killed dozens in an opposition-held town
The regime of Syrian president Bashar al-Assad was responsible for sarin gas attack, claims US, citing independent report.
Russia and the US on oppositie sides over Syria chemical weapons inquiry
Syria claims Israeli jets struck a military base. Monitoring group claims the site was a chemical weapons facility.