The three allies will brief North Atlantic Treaty Organisation envoys on Saturday about their co-ordinated airstrikes.
"We confined it to the chemical weapons-type targets", he said.
Trump says US, allies will launch "precision strikes" until the Syrian government stops the use of chemical weapons.
"The trio strikes started at 3:55 a.m. (Syria local time), launching roughly 110 missiles against Syrian sites in Damascus and nearby areas", the Syrian Armed Forces noted in a statement. The mechanism would look at cases where the OPCW fact-finding mission has established chemical weapons were used or likely used.
Despite severely damaging the infrastructure with the strikes, McKenzie said the Pentagon would not rule out that the Assad government still had capability to use such weapons again.
Syrian state TV has broadcast images of the destruction at the research centre that was targeted.
A British Royal Air Force (RAF) Tornado pilot returns to its base on Cyprus after completing its mission in Syria on April 14.
The OPCW itself had declared that the Syrian government's chemical weapons stockpile had been removed in 2014, only to confirm later that sarin was used in a 2017 attack in the northern town of Khan Sheikhun.
The images shown on Al-Ikhbariya TV are the first of one of the targets.
Though Israel has at times urged stronger US involvement against Assad and his Iranian and Lebanese Hezbollah reinforcements in Syria, it voiced backing for Saturday's air strikes by Western powers.
"From the point of view of the president, this was aggression and we share this position", Russia's TASS news agency quoted lawmaker Sergei Zheleznyak as saying after the meeting with Assad in the Syrian capital Damascus. The Syrian regime and its ally Russian Federation have issued various denials. They say the strikes are punishment for killing dozens of people, many of them women and children, with banned toxic munitions.
On Saturday, the Syrian army said the regime had retaken all of Eastern Ghouta after the last rebels left Douma.
The airstrikes are a "dangerous development", which could be be exploited by "terrorists", Iraq's foreign ministry said.
In a telephone conversation with his Iranian counterpart Hassan Rouhani, Putin and Rouhani agreed that the Western strikes had damaged the chances of achieving a political resolution in the seven-year Syria conflict, according to a Kremlin statement.
Germany's chancellor said the allied strikes in Syria were a "necessary and appropriate" response.
The USA, France and Britain presented a new draft resolution on the investigation of chemical attacks in Syria in the UN Security Council, as AFP reported. The National spoke to Brian Stewart with the Munk School of Global Affairs and Thom Nichols, a professor at the U.S Naval War college where he teaches on national security, to get their thoughts on the potential fallout of the co-ordinated strikes.