Israeli military forces were massing along the border with the Gaza Strip Wednesday evening ahead of a possible incursion into the coastal enclave, an Israeli Defense Forces (IDF) spokesperson said.

The spokesperson, Brig. Gen. Pauli Mordechai, confirmed that Israeli army battalions are making their way to the border, and call-up orders for reserve-service soldiers have been issued, readying towards a prolonged operation within the Gaza Strip.

"All options are on the table. If necessary, the IDF is ready to initiate a ground operation in Gaza," the spokesperson said.

"The days we face in the south will, in my estimation, prove protracted," Mordechai told Israeli Channel 2 television.

The IDF announced earlier Wednesday the commencement of " Operation Pillar of Defense", which officially aims to target Hamas' top leadership, as well as the organization's infrastructure in Gaza, including its stocks of rockets, training camps, rocket-launching sites and police stations, among others.

The announcement came as an Israeli airstrike that killed head of Hamas military wing Ahmed al-Jaabari while he was traveling in a car, prompting the Islamist organization, which seized the control of Gaza in 2007, to "declare war" on Israel.

"The IDF has commenced airstrikes, based on pin-point intelligence, and we have started targeting military officials like Jaabari, who has Israelis' blood on his hands, and at the same time we started to damage their (Hamas') long-range missile stacks, that can reach a distance of 40 km," said Mordechai.

A military source told Xinhua that they could neither confirm nor deny reports that a ground operation may possibly commence this evening, depending on developments.

Several tank brigades and infantry troops units have already deployed along the border, according to local media.

The army has reportedly began to issue emergency call-up orders to reserve soldiers, according to a Channel 10 report.

Military operations are currently limited to bombing sorties over Gaza targeting Hamas' capability to fire long-range missiles and rockets in coming days, according to the army.