Scores of pro-Palestinian protesters on Wednesday night clashed with police outside the national headquarters of the Democratic Party in Washington that forced a lockdown of nearby offices of the United States Congress.

"Our officers are working to keep back approximately 150 people who are illegally and violently protesting" near the party offices, the US Capitol Police said in a post on X, formerly Twitter.

"Officers are making arrests."

Police escorted legislators who were at the Democratic National Committee offices at the time out of the building to safety.

The protesters were calling for a ceasefire and an end to military activity by Israel in the Gaza Strip.

Six police officers were treated for injuries "ranging from minor cuts to being pepper sprayed to being punched," Capitol Police posted later in the evening after protesters were cleared out.

"Was just evacuated from the #DNC after pro-terrorist, anti-#Israel protestors grew violent, pepper spraying police officers and attempting to break into the building," California lawmaker Brad Sherman posted on X.

Another legislator, Sean Casten of Illinois, chided the protesters for "blocking all entries to a building with multiple members of Congress in it," which he said left police dangerously unaware of their intent.

Casten posted on X that he, too, was "rescued by armed officers."