"They agreed it was vital that the use of chemical weapons did not go unchallenged, and on the need to deter the further use of chemical weapons by the Assad regime", a Downing Street spokesman said in a statement.
But she said the U.S. holds Russian Federation and Syria responsible for the incident.
"WHO demands immediate unhindered access to the area to provide care to those affected, to assess the health impacts, and to deliver a comprehensive public health response", he added.
The Russian military said it had observed movements of US Navy forces in the Gulf.
The rest of the world is braced for an expected strike by the United States and its allies against Syria, as Trump taunts Moscow with the prowess of American weaponry and a Kremlin envoy warns that Russian Federation could shoot U.S. missiles down. The prospect of a military escalation in Syria comes after members of the United Nations Security Council failed to agree on a concerted global response on Tuesday.
When - or if - the United States does take action against Syria, the message will be heard loud and clear in Damascus: Using chemical weapons to kill innocent people triggers a righteous US military response.
"France will not allow any escalation that could harm the stability of the region as a whole but we can't let regimes that think they can do everything they want, including the worst things that violate global law, to act", Macron said.
On Capitol Hill, Democrats grilled Defense Secretary Jim Mattis on the legality and constitutionality of Trump ordering an attack on Syria without explicit authorization from Congress. Mattis insisted it would be justified as an act of self-defense; he insisted he could not talk about military plans because an attack "is not yet in the offing".More news: Cleveland Cavaliers vs. Indiana Pacers - 4/15/18 NBA Pick, Odds, and Prediction
The United Nations warned world powers against letting the crisis over an alleged chemical attack against civilians in Syria from "spiraling out of control" after US President Donald Trump said "missiles will be coming". In the year since Trump's Tomahawk attack, Assad appears to have used poison gas, showing that a USA response has its limits.
National security experts anxious about whether strikes would actually serve to deter Assad.
Mrs May is expected to ask her cabinet to approve a form of British participation in action led by France and the United States, aimed at Syrian President Bashar al Assad's chemical weapons infrastructure.
Since Saturday, when images of ashen toddlers struggling for breath emerged from Douma - the main city in the Eastern Ghouta enclave near Damascus that has been a crucible of revolt against Bashar Al-Assad's regime - there has been a sustained military buildup in the eastern Mediterranean.
Assad said Thursday that Western threats to strike Syria are based on "lies" and seek to undermine his forces' advances near Damascus.
Assad spoke during a meeting with Ali Akbar Velayati, foreign policy advisor to Iran's supreme leader Ayatollah Ali Khamenei, and other officials. That sealed a major victory for Assad in the war, crushing a protracted rebellion in the eastern Ghouta region near the capital Damascus.
According to the SANA news agency, the meeting took place on Thursday. It was unclear if his remarks reflected unease about Trump's apparent move toward military action.