Vandals tore down posters of Israeli hostages hung on the wall outside the Capitol Hill office of a Democratic lawmaker on 4 July, his office said on Friday.
Congressman Brad Schneider called the vandalism “a vile act of hate”.
The posters included photos of more than 100 people, eight of them Americans, taken as hostages by Hamas during the 7 October 2023 attack on southern Israel.
Capitol police say they are aware of the vandalism incident outside the congressional office and are investigating.
Mr Schneider, a pro-Israel Democrat from Illinois, posted a photo on X, formerly Twitter, showing the posters shredded and tossed across the hallway.
“This was a shameful act on any day, but especially on July 4, our country’s Independence Day,” he wrote.
“Sadly, it was but one of many hateful, un-American actions that took place across the country on the day we celebrate freedom and democracy.”
The incident comes less than a week after pro-Palestinian protesters held an overnight rally outside Mr Schneider’s Highland Park home in Illinois.
The lawmaker said masked demonstrators banged drums, blew horns and screamed antisemitic chants outside his home.
Police dispersed the crowd of around 40 protesters after several complaints from neighbours.
“These actions don’t advance peace,” Mr Schneider said.
“Instead, they play directly into the hands of Hamas terrorists enabling them to continue to hold hostage not only those they kidnapped from Israel, but all civilians in Gaza as well.”
The war was triggered by Hamas’s unprecedented attack on Israel on 7 October in which Hamas-led gunmen killed about 1,200 people and took 251 others back to Gaza as hostages. Over 100 were released during a November cease-fire.
At least 38,010 Palestinians have since been killed in Gaza as a result of Israel’s offensive, according to the territory’s Hamas-run health ministry.