Family members said 20-year-old Hashem Alagha and 18-year-old Borak Alagha were inside a home in Gaza when Israeli Defense Forces raided the home and detained the two men. Family said they were born and raised in Lombard before moving to Canada at a young age.
The State Department said they are still American citizens.
Their cousin Yasmeen Elagha said their father Ahmed, who is a Canadian citizen, was also detained. She said he once owned a beloved juice shop before along Roosevelt Road before the family returned to Gaza in 2005.
Elagha is trying to comfort her grandparents, who arrived safely Thursday afternoon in Chicago's west suburbs from Gaza.
Elagha said in the days since they escaped, Israeli soldiers stormed her cousins' home in west Khan Younis. She said she got a frantic call from her aunt about the raid late Wednesday night.
"Five a.m. and Israeli soldiers broke down the door, stormed the house, detained all the men. Confiscated all electronics. Destroyed the home from inside, slashed tires," she said.
The IDF has not released any information on the reason for the raid.
The conditions of the men and why they were detained have not been released.
"We are aware of these reports and we are currently seeking additional information, but I don't have any additional information to share and would not be able to at this point, given privacy considerations," said State Department Deputy Spokesperson Vedant Patel at a press briefing.
"Obviously, this is the kind of thing to take very seriously. So, we'll be talking to our Israeli counterparts and trying to get information, more context here about what happened," said Admiral John Kirby.
"I need my family to be immediately released from Israeli custody and be evacuated," Elagha said. "I've been so terrified that the worst would happen and now the worst has happened and it can only get worse from here."
The news comes at a sensitive moment in US-Israeli relations. On Wednesday, US efforts to pressure the Israeli government toward a "humanitarian pause" in Gaza received a blow when Israeli Prime Minister Benjamin Netanyahu dismissed a counterproposal from Hamas as "delusional."
US Secretary of State Antony Blinken, who visited Israel on Wednesday said negotiations toward an agreement would continue.
The CNN Wire contributed to this report