Occupied Jerusalem: Gaza fighters barraged southern Israel with rockets and mortars Wednesday, drawing retaliatory Israeli airstrikes in a worrisome escalation of the gravest hostilities in the area since Israel went to war in the Palestinian territory two years ago.

Israeli Prime Minister Benjamin Netanyahu vowed decisive action against fighters and suggested that future operations would not be surgical.

"No state would tolerate ongoing rocket fire on its cities and its citizens, and the state of Israel obviously will not tolerate it," Netanyahu said in parliament following the latest escalation.

A text message from Gaza's Hamas rulers said the territory's prime minister had been in contact with Palestinian factions trying to keep the postwar truce from unraveling.

The Islamic Jihad group said it fired rockets at four Israeli cities to avenge Israel's killing of eight of its fighters and civilians in Gaza the day before. The group said one of its fighters was killed Wednesday in an Israeli airstrike, and Israeli police said an Israeli civilian was wounded by rocket shrapnel in southern Israel's largest city, Beersheba.

A small faction allied with Hamas group claimed responsibility for a volley of mortars that struck Israel.

The killing of three children and their uncle Tuesday in what Israel called an errant shelling dramatically escalated the recent flare in violence. Hamas declared a day of mourning Wednesday and appealed to all Gazans to take part in the day's funerals.

Dozens of weeping women gathered at the house of three of the victims. Pieces of flesh stuck to the outer wall of the house, which was pocked by shrapnel.

Relatives fired their personal weapons into the air in mourning.

Thousands, meanwhile, participated in the funerals of the four Islamic Jihad fighters killed on Tuesday.

Israel and Hamas have largely observed a truce since the Israeli military offensive in Gaza ended in January 2009. But with the ceasefire fraying in the past week, Netanyahu threatened to respond vigorously to the stepped-up attacks from Gaza.

"It's possible that blows will be exchanged, it's possible it will continue for some time. But we are very resolved to strike at terror elements and block their ability to hurt our citizens."

Netanyahu did not elaborate. But Israel Radio reported that he planned to huddle with security officials to discuss strategy.

Earlier in the day, Israeli Home Front Minister Matan Vilnai predicted that a military confrontation with Hamas was "only a matter of time".

"We are taking all appropriate steps in this direction," Vilnai told Army Radio.

The Hamas text message said Gaza Prime Minister Esmail Haniya had made a round of calls to leaders, including Islamic Jihad chief Ramadan Shalah, trying to defuse the violence.

Both Israel and Hamas are thought to be reluctant to engage in another war, after the 2009 conflict killed hundreds of Palestinian civilians and heavily damaged thousands of homes and businesses.

But although the war inflicted heavy damage on Hamas, the group has replenished its arsenal with bigger and better weapons. Last week, Israel intercepted a cargo ship that it said was loaded with sophisticated anti-ship missiles and other arms sent from Tehran to Gaza.

Over the weekend, fighters launched their heaviest mortar barrage against Israel in years following an Israeli airstrike, stoking a new round of violence.

The mortar shells fired Saturday were the same type as those intercepted last week on the cargo ship, Israel says.