At least 13 Israeli and foreign hostages held in the northern Gaza Strip have been killed in Israeli air strikes in the past 24 hours, Hamas's armed wing said Friday.

In a surprise assault early Saturday, Hamas militants stormed Israeli communities near the Gaza border and fired barrages of rockets, in an attack that claimed more than 1,200 lives.

Israel says Hamas has taken more than 150 people hostage, including both civilians and security forces.

"Thirteen prisoners… including foreigners" were killed in five locations targeted by Israeli fighter jets, the Ezzedine al-Qassam Brigades said in a statement.

Israel has rained air and artillery strikes on the blockaded Gaza Strip — a densely populated enclave of 2.4 million people — flattening buildings and killing more than 1,500 people.

According to the Hamas media office in Gaza, at least 500 children are among the dead.

The Ezzedine al-Qassam Brigades had warned this week that "every targeting of our people without warning will be met with the execution of one of the civilian hostages".