The UN Secretary-General, Antonio Guterres, described the use of chemical weapons as "abhorrent", but stressed that member states must act in accordance with "international law in general". Last year, the US carried out the missile attacks on its own.
McKenzie identified the targets as Barzah Research and Development, the Him Shinshar Chemical Weapons Storage Site and the Him Shinshar Bunker Facility.
The Pentagon official said the allied forces' attack was met with no resistance.
Since the USA and its allies attacked Syria Friday in response to alleged chemical weapons attacks on its own people, there has been a significant surge in Russian trolls promoting fake news, the Pentagon announced Saturday.
"I join President Trump in praying for the safety of our war fighters - the finest among us - and our allies as they avenge and deter the use of outlawed chemical weapons in Syria". Civilians and rebel forces abandoned Douma following the latest attack.
Chief Pentagon spokeswoman Dana White says the target choices were "very methodical", calling it a "deliberate decision" to go after chemical weapons manufacturing facilities. That attack, White says, hit a Syrian military air base and was meant to focus on Syria's ability to deliver chemical weapons.
Mattis said he was not aware of any USA losses, and added, "Right now we have no additional attacks planned".More news: Narendra Modi opens health centre under Ayushman Bharat
"Not just to protect innocent people in Syria from the horrific deaths and casualties caused by chemical weapons, but also because we can not allow the erosion of the global norm that prevents the use of these weapons".
According to Foreign Office Spokesperson Dr Mohammad Faisal, Islamabad "condemns the use of chemical weapons anywhere by anyone".
UN Secretary-General Antonio Guterres, who delayed a trip to Saudi Arabia to deal with the Syria crisis, said he had asked special envoy Staffan de Mistura to return to NY as soon as possible to chart a way forward. "Even this week the Russians vetoed a Resolution at the UN Security Council which would have established an independent investigation into the Douma attack".
McKenzie's remarks contradict an earlier assessment by Russian Federation, a key Syrian ally. "To Iran and to Russian Federation I ask: What kind of nation wants to be associated with the mass murder of innocent men, women and children?" "Russian Federation must decide if it will continue down this dark path or if it will join with civilized nations as a force of stability and peace".