Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE reportedly warned the Syrian government on Sunday not to use chemical weapons following reports of chlorine attacks in Ghouta, an area surrounding the capital city of Damascus.

“It would be very unwise for them to use weaponized gas,” Mattis said, according to Reuters. “And I think President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE made that very clear early in his administration.”

The secretary did not threaten action against Syria, even if the chemical attack was confirmed, the news service reported, but noted that the U.S. launched a cruise missile attack last year on a Syrian base following a previous gas attack.

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He did warn the government that President Trump has “full political maneuver room” to take whatever actions he deems necessary, according to Reuters.

The Syrian government has denied that it carried out a chlorine gas attack. Instead, it has accused rebel forces of planning to set up poison gas attacks in order to blame the Syrian government.

Mattis also criticized Russia for supporting the government's efforts to regain control of rebel-controlled areas of the country.

“Either Russia is incompetent or in cahoots with [Syrian President Bashar] Assad. There’s an awful lot of reports about chlorine gas use or about symptoms that could be resulting from chlorine gas,” Mattis said, according to Reuters.

The United Nations High Commissioner for Human Rights said that the Syrian government’s attacks on Ghouta likely constitute war crimes.

As the Syrian civil war enters its eighth year, the Syrian government has said it will not let up its campaign in eastern Ghouta.