Seven Palestinians were killed, including the commander of Hamas military wing, in a series of Israeli airstrikes on the Gaza Strip Wednesday afternoon.

The airstrikes came as Israel announced the beginning of a large-scale military operation in Gaza called "Operation Pillar of Defense".

In the first airstrike, Israeli aircraft targeted the car of Ahmed al-Jaabari, head of Ezz el-Deen al-Qassam Brigades, and killed him and his escort in Gaza City.

The other airstrikes, targeting training sites of Palestinian militant groups and open spaces which Israel said were used to store rockets, killed five civilians, including a one-month-old toddler and two girls aged at seven and 20 respectively.

Hamas said the killing of al-Jaabari was "a declaration of war. "

Israel "committed a dangerous crime and broke all redlines," said Fawzi Barhoum, a spokesman for Hamas. "The Israeli occupation will regret and pay a high price."

Meanwhile, Palestinian President Mahmoud Abbas called for an urgent meeting of the Arab League (AL) to discuss the escalation in Gaza and prevent a large-scale Israeli operation.

The surge in violence broke a day of relative calmness that prevailed in the area after days of cross-border exchange of fire between Israel and Palestinian militant groups.

Al-Jaabari is the highest-ranking Hamas member to be killed by Israel since the end of Operation Cast Lead, a three-week Israeli military operation in Gaza that saw the death of as many as 1,400 Palestinians in December 2008 and January 2009.

The death of al-Jaabari, 52, is highly expected to set off a fierce surge in violence in which Hamas is likely to use a large portion of its military capacity in attacking Israeli targets, possibly by using longer-range rockets.

Since the end of Operation Cast Lead, Hamas has observed an unofficial ceasefire with Israel and has rarely participated in the waves of cross-border fighting, where smaller factions were the main players.

Al-Jaabari 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.

Al-Jaabari survived several Israeli raids that targeted him, the most serious one in 2004, when the airplanes hit his house, killing three of his relatives and one of his sons.

In 1982, Israel arrested al-Jaabari for being an active within Fatah movement. After his release in 1995, he joined Hamas and ran a Hamas charity taking care of prisoners.

He played the key role in negotiations that led to releasing Israeli soldier Gilad Shalit, who was captured by Hamas in 2006, in exchange for more than 1,000 Palestinian prisoners. The swap took place in two phases in 2011 and 2012.