The Israeli Defense Forces (IDF) has called up more than 16,000 reservists, bringing the total number of reservist troops to 86,000, amid intensifying fighting in the Gaza Strip region.

The latest move is meant to give the Israeli forces "some breathing room", a senior military official was quoted as saying in local dailies.

Meanwhile, the US has reaffirmed its support for the Israeli side.

US Secretary of Defence Chuck Hagel held a telephone conversation with his Israeli counterpart Moshe Ya'alon assuring the "US's support for Israel's security and its right to defend itself".

A statement from Hagel's office read: "Secretary Hagel also expressed the United States's continued concern about the rising number of Palestinian civilian deaths and loss of Israeli lives, as well as the worsening humanitarian situation in Gaza."

"Secretary Hagel stressed the need for a humanitarian ceasefire that ends hostilities and leads to a permanent cessation of hostilities based on the November 2012 ceasefire agreement, and reaffirmed the US view that any process to resolve the cries in Gaza in a lasting and meaningful way must lead to the disarmament of Hamas and all terrorist groups."

In a separate development, the US has allowed Israel to source grenades and mortar rounds from a local US stockpile as part of a bilateral agreement between the two countries.

Pentagon's press secretary Rear Admiral John Kirby said: "Both munitions had been in WRSA-I [War Reserves Stock Allies-Israel] stock for a few years, well before the current crisis. All stocks in WRSA-I, as required by law, are 'in excess of US requirements'. Issuing munitions from the WRSA-I stockpile was strictly a sourcing decision and White House approval was not required."

The Israel-Gaza conflict, which began on 8 July, has only shown signs of escalating despite several ceasefire attempts.

On Wednesday, 30 July alone, at least 129 Gazans were killed and more than 200 injured in the Israeli offensive.

The IDF said they targeted at least 20 sites in Gaza overnight. Local reports suggest a mosque near a school run by the United Nations Relief and Works Agency for Palestine Refugees was hit.

So far, at least 1,400 Palestinians, mostly civilians, have been killed in the fighting, according to Gaza health ministry figures.

On the Israeli side, 56 soldiers and two civilians have been killed.

Israel's Channel Two reported that some 300,000 residents in southern Israel have fled the region since the beginning of the conflict.