"I pray that he would keep our country at peace and not exaggerate or exacerbate the challenges that come up with North Korea, in Russia, or in Syria," Carter told The Associated Press about Trump's recent threats.

"I hope he realizes very profoundly as I did, and as other presidents have done," Carter continued, "that any nuclear exchange could involve catastrophe for all human beings."

Carter pointed out that even a military attack that doesn't escalate into a nuclear exchange "is a dangerous thing" that can unleash unpredictable consequences.

Anti-war activists are also pressuring Trump to proceed cautiously.

"There is no proof yet of a Syrian government gas attack," noted Veterans for Peace President Gerry Condon. "Even if the reports are true, a military response will only lead to more death and destruction, and dangerous escalations."