Hamas militants pounded southern Israel with a barrage of rockets Wednesday, hours after Israeli soldiers killed six gunmen in new violence that threatened a five-month-old truce that has brought relief to both Gaza and southern Israel.

The clashes began late Tuesday after Israeli forces burst into Gaza to destroy what the army said was a tunnel being dug near the border to kidnap Israeli troops.

Despite the outbreak of violence, both the Israeli authorities and officials with Gaza's Hamas government said they wanted to restore the calm that has largely prevailed for five months.

After the Israeli incursion, Hamas gunmen battled Israeli forces and Gaza residents reported hearing explosions, gunshots and helicopter fire. One Hamas fighter was killed, prompting a wave of mortar fire at nearby Israeli targets.

An Israeli airstrike then killed five Hamas militants who the army said were preparing to fire mortar shells. Hamas responded with the rockets.

A spokesman for Hamas, Fawzi Barhoum, said the rockets were in "response to Israel's massive breach of the truce."

"The Israelis began this tension, and they must pay an expensive price," Barhoum said. "They cannot leave us drowning in blood while they sleep soundly in their beds."

The Israeli military said 35 rockets were fired, including one that reached the coastal city of Ashkelon, about 15 kilometers, or 10 miles, north of Gaza - underscoring the militants' growing ability to strike deeper into Israel.

The police said the rocket landed in an empty area and there were no reports of injuries or property damage. But the army said four soldiers were wounded, two moderately, in the border fighting.

The violence was the worst since Israel and Hamas agreed to an Egyptian-mediated truce in June.

In scenes not seen for months, Gaza residents crowded into hospitals, as ambulances delivered the dead and wounded. Grieving militants in military fatigues fired rounds of automatic weapons into the air to commemorate their fallen comrades. Over Gaza City, the thudding sound of rockets being fired into Israel was audible. Unmanned Israeli aircraft, often used to target militants, buzzed overhead.

While Israel and Hamas blamed each other for the violence, neither would say the truce was over.

"We want to see the quiet in the south continued," said Mark Regev, the Israeli government spokesman. "This operation was in response to a Hamas intrusion of the quiet and we hope we won't see an escalation here."

Barhoum, the Hamas spokesman, said the militant group was in touch with Egypt to try to restore calm.

Israel has little appetite for a return to the rocket barrages that have made life in southern border towns unbearable in recent years, while Hamas is interested in strengthening its hold on power in Gaza. Hamas seized control of the coastal strip in June 2007.

Israeli defense officials said they had discovered a 300-meter, or a 1,000-foot, tunnel days ago and concluded that the passage was to be used for a kidnapping. Hamas is still holding an Israeli soldier whom militants captured in a cross-border raid more than two years ago.

The officials, speaking on condition of anonymity because the information was classified, said Defense Minister Ehud Barak approved the operation Tuesday. Defense officials said they knew the raid could jeopardize the cease-fire, but concluded that Gaza's Hamas rulers would have an interest in restoring the calm.

The Israeli Army said a special unit moved about 300 meters into Gaza late Tuesday and destroyed the tunnel.

Also Wednesday, an Israeli work crew knocked down a Palestinian home in East Jerusalem, shortly after the police subdued a crowd of stone-throwing protesters trying to prevent the demolition.

Israel said that the structure did not have proper building permits. Critics say that the permits are virtually impossible to obtain and that the demolitions are part of an Israeli policy to limit Palestinian population growth in the disputed city.