General Joseph Votel, the commander of the U.S. Central Command which coordinates anti-Daesh operations in Iraq and Syria, reportedly canceled a public appearance in New York planned for Thursday, according to the national security reporter for the Daily Beast Spencer Ackerman.

The cancellation comes after U.S. President Donald Trump taunted Moscow to "get ready" for "nice and new and 'smart'" missiles coming to punish Syria for a purported chemical attack on Saturday that killed at least 40 people. The president's tweet followed Russia's warning that it will strike at incoming U.S. missiles and their launch platforms.

U.S Defense Secretary James Mattis also said Wednesday the Pentagon is ready to provide options for a Syria strike in response to a suspected chemical attack, but noted the U.S. and its allies are still gathering information.

"We are still assessing the intelligence, ourselves and our allies, we are still working on this," Mattis said when asked if he had seen enough evidence to blame the Assad regime for the alleged chemical attack in Douma.

"We stand ready to provide military options if they're appropriate as the president determined."

Meanwhile, Department of State Spokeperson Heather Nauert said Wednesday on Twitter: "Reports from contacts on the ground in Douma are credible and will be investigated by the independent OPCW fact-finding mission. This was a barbaric attack and the international community must hold any party that uses chemical weapons accountable. We will stand up for the people of Syria."