The Israel Defense Forces fired on the Gaza Strip Friday, killing nine, Palestinian sources said. 

The Israeli air strikes reportedly killed four Hamas militants, one of them a commander,  and five Palestinian civilians on Friday as a fresh spike in cross-border violence continued for a second day.

The IDF said it had "identified two terrorist squads from Hamas" and hit them from the ground and air.

An elderly Palestinian and two women died when their house in Khan Younis was hit and three other women were wounded, hospital sources said.

Following the IDF attack in Gaza, a barrage of rockets and mortar shells was fired at Israeli towns near the Gaza Strip, and one of the shells exploded in a chicken coop in the Eshkol Regional Council in the Negev.

Rockets were fired near the south Israel city of Ashkelon, and the Iron Dome missile defense system was successful at intercepting three of them. One rocket fell in an open area near Ashkelon, no one was hurt.

Later in the day, two mortars were fired at a Negev town and two additional mortars exploded in open areas. Although no one was hurt, the mortars exploded near homes and chicken coops, causing damage.

On Thursday, IDF strikes in Gaza resulted in the death of five Palestinians, after Gaza militants fired an anti-tank missile at an Israeli school bus, wounding two people.

Hamas announced Thursday that a unilateral cease-fire on the part of all militant factions in the Gaza Strip was to come into effect at 11 P.M. local time, following a meeting between the factions.

Two years of low-level skirmishing on the border escalated suddenly last month when Hamas fired a barrage of rockets at Israel, triggering a surge of fighting.

Analysts in Gaza said Hamas wanted to bolster its claim to leadership of the divided Palestinian national movement and divert attention from popular demands - fueled by the 'Arab Spring' - for an end to the split with its Fatah rivals.

But it had miscalculated Israel's response.

That spurt of violence subsided, but fighting flared again on Thursday when Hamas gunmen fired an anti-tank missile at an Israeli school bus, wounding two. Israel retaliated with planes and armored forces, killing five Palestinians.

Hamas took responsibility for the bus attack, and an Israeli analyst said it was plainly smarting from recent setbacks, including an April 2 Israel airstrike that killed three Gazans, and which it had vowed to avenge.

But firing a long-range anti-tank weapon at a clearly marked school bus may have been a further miscalculation.

"Red lines were crossed," Tal Russo, head of Southern Command, said on Israeli army radio.

The United Nations and European Union on Friday voiced concern over the rising tensions and called on the sides to show restraint and bring an end to the latest round of fighting.