President Donald Trump has warned Syria's government the US is "locked and loaded" to strike again if it carries out chemical attacks.
The warning came after the US, UK and France struck three Syrian sites in response to a suspected deadly chemical attack in the town of Douma a week ago.
Syria denies any chemical use and says that attack was fabricated by rebels.
A UN Security Council vote brought by Syria's ally, Russia, to condemn the US-led strikes was rejected.
The wave of strikes represents the most significant attack against President Bashar al-Assad's government by Western powers in seven years of Syria's civil war.
While Western powers have supported rebels from early on in the war, they have not intervened against Syria directly.
After the failure of the Russian motion, the US, UK and France circulated a new draft resolution to UN Security Council members, calling for an independent investigation into Syria's alleged use of chemical weapons, AFP news agency reported.
A similar previous plan had been vetoed by Russia.
UK Prime Minister Theresa May has blamed Russian obstruction for the need to launch military strikes, saying they left "no practicable alternative".
Read more on BBC.