Palestinian children inspect a home in Beit Lahiye where two of their schoolmates were killed in an Israeli airstrike on March 12, 2016. (Photo by Mohammed Saber/EPA)

A 6-year old Palestinian girl and her 10-year old brother were killed on Saturday when they were struck by debris after a missile launched by an Israeli aircraft hit near their home in Gaza, medical officials said.

The explosive landed near the children's home in Beit Lahiya, a town near the armistice line that separates Gaza from Israel. Yassin Abu Khoussa, the boy, died right away. His sister, Israa Abu Khosa, was transported to hospital where she later died, Gaza health ministry spokesman Ashraf al Qidra told Reuters.

The Israeli military said in a statement that its aircraft targeted four militant training camps in the area in response to rockets that were launched into southern Israel on Friday. No casualties were reported in the rocket attack.

Lieutenant Peter Lerner, a spokesman for the Israeli Defense Forces, defended the Gaza airstrike, and told Reuters that Friday's rocket launch was an attempt by Hamas militants to "threaten the security and safety of the people of southern Israel." Since the beginning of January, militants have fired seven rockets into Israel, according to the Israeli military.

"The (military) will continue to act to protect against those who threaten innocent lives and Israel's sovereignty," Lerner said.

Qassam Brigades, the armed wing of Hamas, released a statement late on Saturday vowing retaliation for the deaths of the two children. "Their blood will not be shed in vain," the group said.

The once-besieged Beit Lahiya area has enjoyed a period of relative peace, as the Israeli-Palestinian conflict has shifted away from Gaza's frontlines and into the West Bank and Jerusalem. The 50-day Gaza war in 2014 between Hamas and the IDF killed 2,139 Palestinians, mostly civilians, including over 490 children. Six Israeli civilians and 64 soldiers were also killed.

Last week, US Vice President Joe Biden met with Israeli officials to negotiate US defense aid, which is currently worth about $3 billion annually. Looming large over the vice president's visit was the recent wave of mostly Palestinian attacks in Israel. On the day of Biden's arrival, an American tourist was stabbed to death on a Tel Aviv boardwalk. The Israelis say the assailant was Palestinian.

Israel initially requested that their annual defense aid be raised to $5 billion, but have since set their sights on $4.5 or $4 billion.

"We're committed to making sure that Israel can defend itself against all serious threats," Biden told reporters after meeting with Israeli president Benjamin Netanyahu. Biden added that Israel's "very, very tough neighborhood, a tough and changing neighborhood" necessitated US support.