One day after White House Press Secretary Sean Spicer warned that the use of barrel bombs in Syria would provoke an additional U.S. response, opposition activists say the regime of President Bashar al-Assad is, in fact, dropping the deadly weapons.

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Syrian helicopter gunships deployed as many as eight barrels loaded with explosives over the city of Daraa after rebel fighters stormed the government-held area, according to the Britain-based Syrian Observatory for Human Rights. The military dropped additional barrel bombs over rebel-held areas in Hama province farther north, the activists said.

The extent of the damage and destruction was unclear.

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Spicer said Monday at the White House that President Trump stood ready to take more action in Syria if necessary, days after the Pentagon reported it launched nearly 60 Tomahawk missiles on a government-controlled base. "If you gas a baby, if you put a barrel bomb in to innocent people, I think you will see a response from this president," Spicer said.

The Trump administration quickly moved to clarify that Spicer was not effectively drawing any new "red lines." A White House statement read, "Nothing has changed in our posture."

By Tuesday, the fighting on the ground in Daraa had killed as many as 16 pro-government troops including an army colonel, the Observatory said. Activists added that Syrian warplanes were conducting raids on Daraa as well.

Secretary of State Rex Tillerson on Tuesday made the Trump administration's position clear: Time has run out for the Assad regime. "It is our policy for a unified Syria that is governed by the people of Syria. I think it is – it’s clear to all of us that the reign of the Assad family is coming to an end," Tillerson said on the sidelines of the Group of Seven (G-7) meeting in Italy.

Damascus again denied using some of the most powerful weapons seen in the six-year civil war. "We do not use these barrels and they do not exist in the Syrian Arab Army," a Syrian military source told Reuters.

Fox News' James Rosen and The Associated Press contributed to this report.