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."