Gaza rocket squads barraged southern Israel early Thursday, after Israeli undercover forces killed four Palestinian militants in the West Bank. The new violence shattered a recent lull in Gaza fighting and highlighted the fragility of efforts to move Israel and the territory's Islamic Hamas rulers toward an informal truce.

A dozen rockets and two mortars were fired late Wednesday and early Thursday, Israeli security forces said. Two rockets struck a warehouse and soccer stadium in the rocket-weary Israeli town of Sderot, but no one was injured. Israeli aircraft struck a loaded rocket launcher early Thursday, but no Palestinian injuries were reported.

The rocket barrage from Gaza was practically a given after Israeli undercover forces opened fire on a car in the West Bank town of Bethlehem on Wednesday, killing the local Islamic Jihad commander, Mohammed Shehadeh, and three other wanted men. The Israeli military said Shehadeh planned suicide bombings that killed dozens of Israelis.

Militant groups in Gaza have claimed the right to retaliate for Israeli operations in the West Bank, and Islamic Jihad claimed it fired 15 rockets and 10 mortars at southern Israel early Thursday.

The latest spiral of fighting began just hours after Hamas' prime minister in Gaza called for a period of calm with Israel, laying out conditions that would imply limited international acceptance of Islamic militant rule in Gaza.

The offer by Prime Minister Ismail Haniyeh had come amid growing signs that Israel and Hamas were moving closer toward an Egyptian-brokered truce deal after a burst of violence in recent weeks killed more than 120 people, nearly all of them Palestinians. The crux of the deal would be the deployment of officers loyal to Hamas' political rival, moderate President Mahmoud Abbas, at Gaza's crossings with Israel and Egypt.

In a speech at Gaza City's Islamic University, Haniyeh demanded an end to Israeli military activity in the Hamas-ruled Gaza Strip, a lifting of Israeli economic sanctions and the opening of Gaza's borders, which have been sealed since Hamas seized control of the area last June.

"We are talking about a mutual comprehensive calm, which means that the enemy must fulfill its obligations," Haniyeh said.. "The Israelis must stop the aggression ... including assassinations and invasions, end the sanctions and open the borders."

Haniyeh also said "all of the factions are involved," signaling that Hamas has the support of smaller militant groups that have often scuttled cease-fire attempts in the past.

But he spoke before the Israeli raid in Bethlehem.

Israel has publicly denied that any informal truce was taking shape, and has repeatedly warned that Hamas would use any lull to rearm.

"We are not in a situation of an arrangement here," Israeli Defense Minister Ehud Barak said during a tour of the Gaza border on Wednesday. "We are in the midst of operations aimed at stopping rocket fire," he added. "There is no change in what we're doing. What awaits us here is more operations."

On Thursday, Barak's political ally, former Deputy Defense Minister Ephraim Sneh, said Hamas had to be toppled before rocket fire would stop.

"Israel will not exist side by side with this Iranian entity 2 miles from Sderot and 6 miles from Ashkelon," Sneh told Army Radio. "There can be no solution without a diplomatic agreement, and there can be no solution without the military wiping out Hamas."

In related news, a Palestinian gunman who killed eight students at a Jerusalem seminary last week was buried late Wednesday, Israeli police spokesman Micky Rosenfeld said. Police had held the body of Alaa Abu Dheim until his family agreed to hold a low-key funeral without media coverage, fearing a mass funeral could spiral into a riot by militant supporters. The burial took place without incident, in the presence of a small number of relatives, Rosenfeld said.

Abu Dheim, a 25-year-old resident of east Jerusalem, was shot dead at the scene of the attack by an off-duty army officer living nearby. No group has claimed responsibility for the attack.