President Donald Trump and Defense Secretary Jim Mattis strongly suggested Wednesday that the U.S. would take action against Syria for an alleged chemical attack against civilians, but both stopped short of specifying the use of military force.

"Militarily, I don't like to say where I'm going, what I'm doing," Trump said at a joint White House news conference with Jordan's King Abdullah II.

"I'm not saying what I'm doing one way or the other," Trump said, but added that the scenes of writhing and dead children following the attack Tuesday had profoundly changed his attitude toward the regime of Syrian President Bashar al-Assad.

At the Pentagon, Mattis said the suspected chemical attack in the northern Syrian province of Idlib was "a heinous act and will be treated as such." He did not elaborate or respond to further questions at a meeting with Singaporean Defense Minister Ng Eng Hen.

Mattis has sought and been granted approval by Trump for an accelerated campaign against the Islamic State of Iraq and Syria, but the administration's position on Assad and the Russian support for the regime has been unclear.

Any military action against Assad's forces would risk hitting Russian troops, who are closely intertwined with the regime's military.

Outside the northeastern Syrian city of Manbij, Russian troops are on the ground with regime forces and within sight of a small contingent of Army Rangers sent to the town as a "visible presence" to prevent a takeover, according to Army Lt. Gen. Stephen Townsend, commander of Combined Joint Task Force-Operation Inherent Resolve.

In the past, Trump has said he is open to the possibility of declaring and defending safe zones inside Syria for refugees, but the U.S. military has consistently warned of the cost and difficulty of taking on that responsibility amid the six-year-old civil war that has killed more than 400,000 and displaced an estimated 10 million.

Earlier this week, Secretary of State Rex Tillerson said that Assad remaining in power is a matter for the Syrian people to decide. White House Press Secretary Sean Spicer said, "There is a political reality that we have to accept" in terms of Assad's position.

However, Trump said at the joint news conference that "my attitude toward Syria and Assad has changed" as the result of the alleged chemical attack. "I like to think of myself as a flexible person. I do change, and I'm flexible. That attack on children yesterday had a big impact on me."

As he has previously, Trump blamed the crisis in Syria on former President Barack Obama and his failure to take action after stating that a chemical attack would be a "red line" requiring a military response. At the time, Trump tweeted that "there is no upside, tremendous downside" to taking military action against Syria.

"The Obama administration had a great opportunity to solve this problem," Trump said Wednesday. "I now have the responsibility. It is now my responsibility."

The chemical attack "crossed a lot of lines for me -- that crosses many, many lines, beyond a red line," he said.

The Russian Defense Ministry has said that the casualties in Idlib were caused when an airstrike hit a building where chemical weapons were stored by rebel groups.

When pressed on the use of military force, Trump said, "You will see," but added that the Assad regime "will have a message" from the eventual U.S. response. "You will see what the message will be."

Earlier, Nikki Haley, the U.S. ambassador to the United Nations who is now serving as president of the Security Council, condemned the Syrian regime and Russia for the alleged chemical attack and suggested that the U.S. might take military action.

"When the U.N. consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action," Haley said. "For the sake of the victims, I hope the rest of the council is finally willing to do the same. How many more children have to die before Russia cares?"

On MSNBC, veteran diplomat Ryan Crocker, the former U.S. ambassador to Iraq, Syria, Afghanistan and Pakistan, said Trump's remarks on Syria represented a major change from the "America First" rhetoric of the campaign and suggested that he is now an internationalist in the tradition of previous presidents.

"He is emerging, contrary to the campaign, as an internationalist," Crocker said. "I think this is really, really important."

His comments on Syria suggest that Trump now believes that "the U.S. will lead in the international order," Crocker said. "I don't think any of us expected this from him."

-- Richard Sisk can be reached at Richard.Sisk@military.com.