The White House on Monday was forced to clarify a comment made by press secretary Sean Spicer to reporters that seemed to indicate that the U.S. was lowering its threshold for the use of force in Syria.

On Monday, Spicer added barrel bombs to the list of atrocities committed by Syrian President Bashar Assad that could be met with a military response.

"The sight of people being gassed and blown away by barrel bombs ensures that if we see this kind of action again, we hold open the possibility of future action," Spicer said.

Until now, military force had been reserved as a response to the use of chemical weapons only, not conventional weapons. In a follow-up statement, the White House said the administration's position hasn't changed.

"Nothing has changed in our posture," a White House spokesman said. "The president retains the option to act in Syria against the Assad regime whenever it is in the national interest, as was determined following that government's use of chemical weapons against its own citizens. And as the president has repeatedly made clear, he will not be telegraphing his military responses."

The U.S. military strike on Syria's Shayrat airfield was launched last week specifically because the regime's chemical attacks on civilians originated at the airfield.

Spicer's Monday comments caused confusion at the Pentagon. One senior Pentagon official said he believed the threshold for attack had not been lowered.

"I just talked to the secretary this morning, and it's all about chemical weapons with him," that official told the Washington Examiner, referring to Defense Secretary Jim Mattis.

"No idea," said another senior military official when asked if barrel bombs are the new red line. "That would be a policy decision, not military. "

Spicer's pronouncement came as Mattis claimed that any further use of chemical weapons by the Assad regime would be "ill-advised."

"The president directed this action to deter future use of chemical weapons and to show the United States will not passively stand by while Assad murders innocent people with chemical weapons, which are prohibited by international law and which were declared destroyed," Mattis said.

Mattis also spelled out the extent of the damage on the airfield, which came after President Trump ordered two U.S. Navy destroyers in the eastern Mediterranean to shower the airfield with 59 Tomahawk cruise missiles.

"The assessment of the Department of Defense is that the strike resulted in the damage or destruction of fuel and ammunition sites, air defense capabilities, and 20 percent of Syria's operational aircraft," Mattis said. "The Syrian government has lost the ability to refuel or rearm aircraft at Shayrat airfield and at this point, use of the runway is of idle military interest."

Before the Mattis statement, it had been unclear the extent of the damage to the airfield, which was used as a launching point for last week's chemical attack on Syrian civilians in Idlib province. The Pentagon had estimated that about 20 warplanes on the airfield had been destroyed, but the 20 percent figure puts the damage in broader context.