An alt-right group and a group of opponents faced off Saturday night in one of the most raucous White House demonstrations of the Trump presidency, prompted by the missile attack against Syria.

The alt-right group was led by Richard B. Spencer, a white nationalist, who said the Lafayette Square rally was to urge “No more Neocon wars.” He said the group would oppose “further military intervention in Syria.”

Meanwhile, another group, which organized under an antifascist heading, appeared and shouted such slogans as “No ­Nazis, No KKK, No Fascist USA.”

Officers from the U.S. Park Police and the Secret Service stood between the two groups, of about two dozen each.

At the end, police escorted Spencer to a taxi, but he said it was then surrounded.

He said in a Twitter message that the counterdemonstrators “slammed the car until the driver abandoned the vehicle. I was able to escape. I’m totally unharmed.”