U.S. President Donald Trump said on Thursday that he was going to hold meeting on Syria and the decisions on the U.S. response to the suspected chemical weapons attack in Syria will be made "fairly soon." 

"We are having a meeting today on Syria," Trump told reporters at the White House. "We have to make some further decisions, so that'll be made fairly soon," Trump added.

The new remarks by Trump on the deadly incident in Syria's Douma came hours after his tweet in which he refused to specify any timetable for potential U.S. military action on the war-torn country.

"Never said when an attack on Syria would take place. Could be very soon or not so soon at all!" Trump wrote in the tweet on Thursday morning.

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

The Syrian Foreign Ministry has denied the accusations, calling rebels' claims "premeditated pretexts."

U.S. Defense Secretary Jim Mattis told Congress on Thursday morning that he was convinced that there was a chemical attack in Syria.

"I believe there was a chemical attack and we are looking for the actual evidence," the Pentagon chief told the lawmakers.

He also noted that the United States had not made any decision to launch military action in Syria.

Mattis added that Washington would like to have inspectors in Syria "probably within the week," as the evidence could become more difficult to collect when time passed by.

NBC News reported that the U.S. officials said they were "confident" that chemical weapons have been used in Syria though not one-hundred percent sure.

The Syrian Foreign Ministry has reiterated on Thursday the Syrian government's willingness to cooperate with an investigation team into the chemical attack allegations, according to the state news agency.