"I don't rule out anything right now," Mattis told reporters at the Pentagon when asked about the chance of US strikes against Syrian President Bashaar Assad.
Speaking ahead of a meeting with Qatar's Emir Shiekh Tamim bin Hamad al Thani, Mattis said the international community must determine why chemical weapons are still being used in Syria after Russia agreed to serve as a "framework guarantor" for the removal of all chemical arms from the country.
The US defense chief promised to work with "allies and partners from NATO to Qatar and elsewhere" to address the issue.
Earlier on Monday, Syria’s SANA news agency reported that a missile strike targeted Syria’sr T-4 airbase in Homs province, while Russian Defense Ministry said the attack was carried out by two Israeli F-15 fighter jets.
US President Donald Trump accused Russia and Iran of supporting Syrian President Bashar Assad and therefore being responsible for the alleged attack. Syrian officials cited by the SANA news agency said the allegations were merely a provocation by the Jaish al-Islam terrorist group and other militants to prevent the advance of the Syrian government’s army.