David Jackson, Gregory Korte, and Jim Michaels

USA TODAY

PALM BEACH, Fla. — The Trump administration is developing plans to respond to Syria's alleged use of chemical weapons, including possible military action and attempts to remove Syrian President Bashar Assad from power, President Trump and government officials said Thursday.

The Pentagon has developed a number of options, including strikes on Syrian military targets with weapons, such as cruise missiles, according to a U.S. official who asked not to be named because he was not authorized to discuss the planning publicly.

The missiles can be fired from ships or aircraft and guided to targets hundreds of miles away. Such strikes have the advantage of not directly risking U.S. military personnel.

The strikes would be aimed at Assad's military, such as command and control facilities, barracks and airfields, the official said. And the strikes would likely be calibrated to be proportional, meaning they would punish the regime without causing it to collapse, the official said.

Still, it is difficult to predict events once U.S. military power is unleashed in a country as unstable as Syria, where Assad's regime is fighting a six-year-long civil war that has brought foreign powers into the fray.

The Russians and Iranians have forces in Syria aiding Assad, and a U.S. military strike against him risks triggering a broader conflict.

A U.S.-led coalition has been conducting airstrikes in Syria against the Islamic State, one of many groups battling the regime's forces. The U.S. military also has several hundred advisers in the country assisting other rebel groups that are battling the Islamic State.

Until now, the U.S. has take precautions to avoid attacks on Syrian troops or their Russian allies.

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If U.S. strikes are launched against Assad and lead to his regime's collapse, the result could be chaos that the Islamic State militants and other extremist groups in Syria could exploit to create an even more volatile situation in the Middle East.

The military planning follows an attack on a rebel-held city in northern Syria with apparent chemical weapons that killed at least 86 people, 27 of them children. Autopsies on three Syrians who died after being brought to Turkey for treatment suggest the banned nerve agent sarin was used in the attack, the Turkish Health Ministry said.

Turkey, which also is involved in the fighting, has long pushed for Assad's ouster.

Russia said the deaths were caused by a Syrian strike on a terrorist chemical lab, but the U.S., other nations and human rights groups rejected that claim as baseless.

Images of the dead children drew a harsh judgment from President Trump, who vowed Wednesday to respond.

“I don’t want to say what I’m going to be doing with respect to Syria,” Trump told reporters Thursday en route to his Mar-a-Lago estate in Palm Beach, Fla., where he is hosting Chinese President Xi Jinping for a two-day summit.

The threat of retaliation against Syria is an about-face for Trump, who had previously urged the U.S. to support Assad against rebel groups fighting him, many of which are aligned with al-Qaeda.

“I think what happened in Syria is a disgrace to humanity, and he’s there, and I guess he’s running things, so I guess something should happen," Trump said.

"What Assad did is terrible," Trump added. "What happened in Syria is truly one of the egregious crimes and it shouldn’t have happened. And it shouldn’t be allow to happen.”

Trump "is being presented with a lot of options," White House spokesman Sean Spicer said, adding that the president has not signed off on any specific plans.

While Trump held off on saying whether the U.S. would lead a global effort to remove Assad from power, Secretary of State Rex Tillerson said "those steps are underway."

Horrified by photos

Tillerson said the pictures from Syria "just horrified all of us.” He spoke to reporters in Palm Beach, where Trump is meeting with the president of China.

Tillerson said that, given the evidence, there is "no doubt in our minds" that "the Syrian regime, under the leadership of Assad, is responsible for this attack.”

He added "there is no room for him to govern the Syrian people," though any process of forcing out Assad "would require international effort.”

To that end, Tillerson said Russia “should reconsider carefully” its role in supporting the Assad regime.

“We are considering an appropriate response,” he said. “It’s a serious matter that requires a serious response.”

Earlier, a Kremlin spokesman said Russian support for Assad is "not unconditional," although Russia has backed him throughout a brutal civil war that has killed an estimated 500,000 people, left 9 million Syrians homeless and has been marked by numerous regime atrocities the United Nations brands as war crimes.

Meeting with Trump in Florida are Defense Secretary Jim Mattis and National Security Adviser H.R. McMaster.

The White House said Trump has spoken with world leaders about the establishment of "safe zones" for Syrian citizens caught in the civil war.

The Syrian government maintains it didn’t use chemical weapons, instead blaming opposition fighters for stockpiling the chemicals.

Sens. John McCain, R-Ariz., and Lindsey Graham, R-S.C., called for grounding Assad's air force to deny him "a strategic advantage in his brutal slaughter of innocent civilians, both through the use of chemical weapons as well as barrel bombs, which kill far more men, women and children on a daily basis."

The world is "watching to see how our country will respond," McCain and Graham said in a joint statement. "If the President is willing to take the necessary action, he deserves broad bipartisan support, and we will help build it,” they said.

In January, Trump and Russian President Vladimir Putin spoke on the telephone about Syria, and agreed to seek ways to join forces to fight the Islamic State, also known as ISIS.

At the time, McCain warned that Russia could not be trusted, because it was propping up a "murderous regime" in Syria.

