BE'ER SHEVA, Israel -- When Hamas militants stormed into Rotem Mathias' kibbutz in southern Israel last Saturday, the 16-year-old helped his parents barricade the doors of their home with anything they could find -- mattresses and tables. But it wasn't enough.

The militants opened fire at their house, spraying bullets through the windows. Mathias' parents, Shlomi and Deborah, were killed before his eyes.

"The terrorists shot open the door," Mathias, a dual Israeli-American citizen, recalled during an interview with ABC News that aired Wednesday on "Good Morning America."

"They throw a grenade or something that exploded," he continued. "The last thing my dad said is he lost his arm and then my mom died on top of me."

Mathias' parents are among the more that 1,200 people who have died since Hamas launched an unprecedented incursion into Israel from air, land and sea over the weekend. The Israel Defense Forces has since declared "a state of alert for war" and launched retaliatory airstrikes on the neighboring Gaza Strip, a 140-square-mile territory where 2 million Palestinians have lived under a blockade imposed by neighboring Israel and Egypt since Hamas seized power in 2007. Palestinian authorities said at least 1,055 people have died and another 5,184 have been injured in Gaza since Saturday.

Back in Mathias's kibbutz, the teen laid still as he hid under a bloodied cloth for hours on Saturday when Hamas militants stalked his home and later returned to hunt for any survivors. He managed to send a brief text message to extended family members, writing: "Parent's dead. Sorry."

"I just stopped my breathing, I lowered it down as much as I possibly could," Mathias told ABC News. "I didn't move. I was terrified. I didn't make any noise. And I prayed for any god -- I didn't really care which god -- I just prayed for a god that they won't find me."

The militants then set fire to Mathias' home and others in the kibbutz, forcing him to leave. He was eventually found and rescued by Israeli forces.

ABC News met Mathias on Wednesday morning at a hospital in the southern Israeli city of Be'er Sheva where the teen sat shaking beside his older sister, who had also hid throughout the ordeal but was able to barricade herself in a safe room.

The orphaned siblings are now reliant on their grandfather, Ilan, who is mindful of history.

"They came back and -- this is so important -- they wanted to verify that they had killed everybody," Ilan told ABC News of the Hamas militants. "They set the fire and -- this is a story that comes from the Holocaust -- they set the fire to make sure that if there were any survivors, they would exit and they could murder them."

Despite the unspeakable depravity that Mathias and his family have experienced in the past few days, their bonds remain unbreakable and their love for each other is undeniably strong.

ABC News' Morgan Winsor contributed to this report.