WASHINGTON -- US President Donald Trump spoke over the phone with his French counterpart Emmanuel Macron on Sunday, and both sides agreed on a "strong, joint response" to the latest alleged chemical weapons attack in Syria, said the White House.

During the phone call, Trump and Macron "agreed to exchange information on the nature of the attacks and coordinate a strong, joint response," the White House said in a statement.

On Saturday, activists said the Syrian forces used chlorine gas in an attack against Douma, the last rebel-held area in the Eastern Ghouta countryside of Damascus, killing at least 40 people. The accusation was strongly denied on Sunday by the Syrian government.

In Sunday's phone call, both leaders condemned Saturday's attack in Syria and held the Syrian government accountable for "its continued human rights abuses," according to the White House statement.

Trump said in a tweet on Sunday morning that a "big price" would be paid for what he said was a chemical weapons attack in Syria.

He also accused Russia and Iran of being partially responsible for the attack for backing the Syrian government led by President Bashar al-Assad.

The Russian Foreign Ministry on Sunday refuted reports purporting that Syrian government forces used chemical weapons in Douma, calling the allegation "fabrication" and "provocation."