By
"The prime minister spoke to the French president Emmanuel Macron this evening about the horrific attack in Douma, Syria, on Saturday," a Downing Street spokesman said.
"They agreed to keep working closely together on the international response."
The United States says it has proof that Syrian President Bashar al-Assad's regime launched the alleged attack on the then rebel-held suburb of Douma on April 7.
France's UN ambassador Francois Delattre said that in choosing once again to use banned chemical weapons against civilians, Assad's regime had "reached a point of no-return."