Harsh and hardened words and actions have been traded between Islamic Hamas movement and the Israeli army on Wednesday after chief of Hamas' military wing Ahmed al-Jaabari fell prey to an Israeli attack earlier in the day in the Gaza Strip.

Al-Jaabari was killed in an Israeli air raid on his car Wednesday afternoon in Gaza City. According to Hamas, which controls the coastal enclave, the killing of its commander was "a declaration of war" with Israel.

Al-Jaabari is the highest-ranking Hamas member to have been killed by Israel since the end of Operation Cast lead, the three- week-long Israeli military campaign in Gaza that saw the death of as many as 1,400 Palestinians from December 2008 to January 2009.

The 52-year-old has become the virtual leader of Ezz el-Deen al- Qassam brigades after Israel badly wounded the official No.1 commander, Mohammed al-Deif, in an attempted assassination in 2003; and has survived several Israeli raids that targeted him -- the most serious one in 2004 when Israeli airplanes hit his house and killed three of his relatives and one of his sons.

Israel "committed a dangerous crime and broke all redlines," Fawzi Barhoum, a spokesman for Hamas, said of al-Jaabari's assassination. "The Israeli occupation will regret and pay a high price," and "The occupation has opened doors of hell against itself," he said.

A similar response was made by the Islamic Jihad, a smaller militant group, saying the killing of al-Jaabari was a declaration of war against the Palestinians.

Meanwhile, Palestinian President Mahmoud Abbas, for his part, has on Wednesday evening called for, via the Palestinian ambassador to Egypt, an urgent Arab League (AL) meeting to discuss the escalation in Gaza and prevent a large-scale Israeli operation.

However, al-Jaabari's death is still believed to be setting the fuse of a fierce surge in violence in which Hamas might use a large portion of its military capacity in attacking Israeli targets when Israel could act in either proactive or retaliatory moves.

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

Mordechai also said that 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 IDF has commenced airstrikes, based on pin-point intelligence, and we have started targeting military officials like al-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. But several tank brigades and infantry troops units have already been deployed along the border, according to local media.

Palestinian medical sources and witnesses have said that a series of concurrent airstrikes had been fired from Israel on the Gaza Strip shortly after the killing of al-Jaabari, and that at least another six Palestinians, including possibly a son of al- Jaabari and a one-month-old toddler, were killed in Wednesday's violence.

The fresh round of conflict comes after a day of relative calmness following days of cross-border exchange of fire in the strip.

On Saturday, Palestinian militants fired an anti-tank missile against an IDF patrol jeep, wounding four soldiers.

On Tuesday, Israeli Prime Minister Benjamin Netanyahu told mayors of southern Israeli citizens that it was his responsibility to "choose the right time to exact the heaviest price" for the continual rocket fire from Gaza.