"Developments in Syria have changed the situation fundamentally," Johnson said in a statement on April 8, RFE/RL wrote.

"My priority is now to continue contact with the United States and others in the run-up to the G7 meeting on 10-11 April – to build coordinated international support for a cease-fire on the ground and an intensified political process," the statement said.

Johnson added, "We deplore Russia's continued defense of the [Syrian President Bashar al-] Assad regime even after the chemical weapons attack on innocent civilians."

Read alsoContainers for chemical weapons found at Shayrat Air Base in Syria – OSINT expertsHe called on Russia, a key Assad ally, "to do everything possible to bring about a political settlement in Syria and work with the rest of the international community to ensure that the shocking events of the last week are never repeated."

Western countries have blamed Assad's armed forces for the airborne attack dispersing what appeared to be a nerve agent on the town of Khan Sheikhoun on April 4, killing more than 86 people. Syria's government has denied responsibility.

The United States struck a Syrian air base with dozens of cruise missiles early on April 7 in response to the alleged attack.