The White House announced Monday afternoon that there are now 11 confirmed American deaths and more Americans being held hostage.
Among those missing and possibly being held are Judith Tai Raanan and Natalie Raanan of Evanston, who were visiting relatives in Nahal Oz, a kibbutz attacked by Hamas militants Saturday.
READ MORE: Israel strikes and seals off Gaza after attack by Hamas, which vows to execute hostages
Adi Leviatan, Judith Raanan's brother, said he suspects the pair has been taken hostage after not hearing from them since the weekend. The mother and daughter had arrived in Israel on Sept. 2, Leviatan said.
Illinois state records show Leviatan was at one time a licensed esthetician in Evanston but that license is no longer active.
Uri Raanan, Judith's ex-husband and Natalie's father, said his daughter just graduated from Deerfield High School and is just about to turn 18.
Holding back tears over the phone, Uri told the I-Team that Judith and Natalie left Chicago to head to Israel on Sept. 1 to celebrate the Sukkot and Simchat Torah holidays abroad.
This past weekend, Uri said Judith and Natalie traveled to Natalie's grandmother's home in Nahal Oz, the kibbutz that was attacked by Gazan militants Saturday morning.
Uri said in the last text message he received from his daughter on the morning of the Israeli invasion, Natalie said they were "hiding in a bunker or safe room from the bombing" and that she had very bad cell phone reception.
That was the last he heard from his daughter. He said a neighbor of the grandmother said they saw Hamas militants escort both Judith and Natalie out of the house.
Israel increased airstrikes on the Gaza Strip and sealed it off from food, fuel and other supplies Monday in retaliation for a bloody incursion by Hamas militants, as the war's death toll rose to nearly 1,600 on both sides. Hamas also escalated, pledging to kill captured Israelis if attacks targeted civilians without warnings.
In the war's third day, Israel was still finding bodies from Hamas' stunning weekend attack into southern Israeli towns. Rescue workers found 100 bodies in the tiny farming community of Beeri - around 10% of its population - after a long hostage standoff with gunmen. In Gaza, tens of thousands fled their homes as relentless airstrikes leveled buildings.
The Israeli military said it had largely gained control in the south after the attack caught its vaunted military and intelligence apparatus completely off guard and led to fierce battles in its streets for the first time in decades. Hamas and other militants in Gaza say they are holding more than 130 soldiers and civilians snatched from inside Israel.
The ABC7 I-Team spoke with Elton Dixon, a Chicagoan and retired doctor who moved to Israel three years ago.
"I can hear the Iron Dome working around me," he said. "We haven't had any sirens near me. But I do hear the Iron Dome catching rockets and coming into the country. I have friends that live in Jerusalem and they were getting bombarded like a couple hours ago."
The U.S. has already begun delivering critically needed munitions and military equipment to Israel, and the Pentagon is reviewing inventories to see what else can be sent quickly to boost its ally in the three-day-old war with Hamas, a senior Defense Department official said Monday.
The Associated Press contributed to this report.