"Every targeting of our people without warning will be met with the execution of one of the civilian hostages," the Ezzedine al-Qassem Brigades, the armed wing of Hamas, said in a statement.

"The enemy doesn't understand the language of humanity and ethics, so we'll address them in the language that they understand."

Israel has pounded the Gaza Strip over the past three days after Hamas militants surged into southern Israeli towns in a surprise attack that has left hundreds killed.

Militants, who sprayed bullets under the cover of thousands of rockets fired from the Gaza Strip, fled back to the enclave with about 100 hostages.

An Israeli military spokesman said on Monday that details of about 30 hostages have been given to their families.