Trump was also expected to speak with French President Emmanuel Macron, who said on Thursday France had proof the Syrian government carried out the Douma attack and would decide whether to strike back when all necessary information had been gathered.
In the meantime, British Prime Minister Theresa May said she had authorized British armed forces "to conduct co-ordinated and targeted strikes to degrade the Syrian regime's chemical weapons capability".
Blasts were reported in Damascus, Syria, just minutes after President Trump announced that he would be launching an attack in retaliation for last week's chemical attack by Bashar al-Assad on his own citizens.
Trump said that the "massacre" last weekend in Syria "was a significant escalation in a pattern of chemical weapons use by that very bad regime".
The U.S. stance on striking Syria is no clearer, even after President Trump tweeted that missiles "will be coming". Referring to the Syrian leader, Bashar al-Assad, Trump said.
On Wednesday, Trump warned Russian Federation to brace for US engagement in Syria, after a suspected chemical attack in Eastern Ghouta's Douma killed dozens.
Explosions lit up the skies over Damascus, the Syrian capital, as Trump announced the airstrikes from the White House. Syrian television reported that a scientific research centre had been hit.
Speaking to reporters at the White House later in the day, Trump said a decision had not yet been made on a course of action.
As a result, Western officials are instead pressing a moral argument, saying Assad must be stopped from using particularly cruel and outlawed weapons.
Russian Federation has systematically used its Security Council veto to block any move against Syria, which it has backed since 2015 when it helped Assad turn the tables against opposition forces.
"Never said when an attack on Syria would take place", the president tweeted.
The UK Cabinet agreed Thursday "that the Assad regime has a track record of the use of chemical weapons and it is highly likely that the regime is responsible for Saturday's attack", according to the Downing Street statement.
Later, US defence secretary James Mattis told Congress he believed there was a chemical attack in Syria but that the US was "looking for the actual evidence".
The president on Wednesday seemed to confirm future US strikes in Syria when he tweeted that missiles fired at Syria "will be coming, nice and new and 'smart!'"
In another series of tweets on Wednesday, Trump bemoaned the state of relations between the United States and Russian Federation.
Meanwhile, Russia's Embassy to the United Kingdom tweeted a statement by the Ministry of Foreign Affairs' spokeswoman, Maria Zakharova, that denied there was any evidence of a chemical attack.
"Clearly the Assad regime did not get the message previous year", Mattis said.
"We did everything we could in our intelligence assessment and our planning to minimise to the maximum degree ... any chance of civilian casualties".
CNN reported a Western military operation was under way in Syria and that Tomahawk cruise missiles are believed to have been mobilized as was the case in the air raid of April past year.