Defense Secretary Jim Mattis says the Syrian regime would be “ill-advised” to use chemical weapons in the future, foreshadowing a potentially greater US response than the cruise missile strike that was carried out last week.

Mattis said in a statement that the strike, which consisted of 59 Tomahawk cruise missiles targeting the Shayrat air field on April 6, was a “measured response” to the Assad regime’s use of chemical weapons.

In a break from his predecessor, President Donald Trump quickly authorized strikes against the Syrian government —a first for the US. According to Mattis, it was meant to deter future chemical weapons use, while showing the world that the US would “not passively stand by” when such atrocities are carried out.