Army helicopters fired missiles, heavily damaging offices connected to the ruling Fatah movement and roads in the northern part of the territory.
The air assault came just hours after Israeli defence minister Shaul Mofaz ordered the army to begin assembling a security zone in northern Gaza that Palestinians will be barred from entering.
Helicopter rockets slammed into the offices of Palestinian leader Mahmoud Abbas's party at the northern town of Beit Lahiya, causing serious damage but no injuries, Gaza security sources said.
The army said the buildings in Beit Lahiya were used by the Al Aqsa Martyrs Brigades, an armed offshoot of Fatah. Helicopters also hit roads and a bridge used to access sites from where rockets are fired, the army added.
"The objective of targeting these routes is to prevent the passage of terrorists to the rocket launching grounds, and to disrupt the repeated attempts to fire projectile rockets at Israeli targets," it said.
Al Aqsa claimed to have fired rockets into Israel on Monday, one of which landed near a nursery school but none of which caused any damage or injuries.
The Palestinian Authority criticised the raids, with spokesman Nabil Abu Rudeina saying the attacks compromised a de facto truce that the principal militant factions have largely observed since the start of the year.
"The continued aggression and Israeli raids risk sabotaging efforts made by the Palestinian Authority to consolidate the truce," he said.
Abu Rudeina urged Washington to "act quickly to end the Israeli escalation and overturn the Israeli decision to establish a buffer zone in Gaza".
Three months after Israel withdrew all Jewish settlers and troops from Gaza following a 38-year occupation, Mofaz ordered the army to begin setting up a "security strip" as a buffer zone to protect Israel against militant attacks.
The decision would put a "limitation" on Palestinians circulating in northern Gaza, a defence ministry source said late on Monday.
Any Palestinian straying into the zone could be shot by troops from across the border. Television said that helicopters would play a key role in enforcing the "sterile" zone, largely to envelop former Jewish settlements.
Palestinian political and militant leaders have rejected the plan outright.
An Israeli military spokesman said that movement to enforce the security zone could come in the "next few days", with talks still underway to determine logistics.
"In terms of exactly what this zone or strip will be is still being decided upon" in talks within the army and defence ministry, the source said.
After a security meeting on December 22, Prime Minister Ariel Sharon ordered the army to establish the no-man's land.
Local media had reported that the army was awaiting an improvement in the weather before starting to enforce the area, albeit without reoccupying the territory with ground troops.
Palestinian Prime Minister Ahmed Qurei has "categorically rejected" the plans and warned against "the consequences" of the security buffer zone.
Given the somewhat less than watertight Palestinian truce, an upsurge in violence is predicted ahead of parliamentary elections in January.
A spokesman for the radical group Islamic Jihad in Gaza has threatened an upsurge in rocket attacks should Israel go ahead with the plans.
In further evidence of the heady chaos in Gaza, around 30 Fatah gunmen seized the premises of a local authority building in Beit Lahiya, demanding jobs in the rebranded Palestinian security services.
© 2005 Agence France-Presse
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