WASHINGTON - The United States discussed the response to the alleged "chemical attack" in Syria with Britain and France, as the possibility of US military actions against Syria loomed larger on Monday.

The White House said in a statement that President Donald Trump spoke with his French counterpart Emmanuel Macron to continue their coordination on responding to the alleged use of chemical weapons on April 7 in Syria.

The communication came on the heels of Trump's call on Sunday with Macron over the Syria issue, as both leaders "strongly condemned" the "horrific chemical weapons attacks" and agreed to exchange information on the nature of the attacks and coordinate a "strong, joint" response.

According to a statement of State Department spokesperson Heather Nauert, US Acting Secretary of State John Sullivan spoke by phone twice on Monday with British Foreign Secretary Boris Johnson to discuss the attack in Douma, Syria, which killed dozens of civilians and injured several hundred more.

They discussed the international community's response and potential further steps the two governments might take in coordination with other partners.

Also on Monday, Trump said that the United States is "going to make a decision tonight or shortly thereafter" on the Syria incident.

"We're making decisions as to what we do with respect to the horrible attack that was made near Damascus. And it will be met. And it will be met forcefully," he said.

The White House host added that "we can't let that happen in our world, especially when we're able to -- because of the power of the United States -- we're able to stop it."

Speaking of the US possibility to strike Syria, US defense chief James Mattis also said on Monday that "the first thing we have to look at is why are chemical weapons still being used at all, when Russia was the framework guarantor of removing all the chemical weapons."

"And so, working with our allies and partners, from NATO, to Qatar and elsewhere, we are going to address this issue," he added.

Mattis refused to rule out possibility of the US military actions, including the launching of airstrikes against Syria.

Activists, local rescuers and rebels in Syria claimed that Syrian forces used chlorine gas in the attack on Saturday against Douma, in the rebel-held area near Damascus.

The Syrian Foreign Ministry responded to the rebels' claims of chemical weapons used by the Syrian army in Douma district near Damascus as "premeditated pretexts," according to state news agency SANA.

The ministry said the allegations have been planned beforehand to prolong the lives of the "terrorists" in Douma. The Syrian government has denied the allegations and called it "fake news".