GAZA CITY, Gaza Strip - Palestinian militants ambushed an Israeli ground force in the northern Gaza Strip on Wednesday, killing three soldiers in a clash that prompted Israel to delay the resumption of crucial fuel deliveries to the impoverished Palestinian area. Four Hamas gunmen also were killed in separate clashes.

Intense battles took place throughout Gaza on Wednesday, making it one of the bloodiest days of fighting since Israel ended a military offensive in early April.

At least five Palestinians and three soldiers were wounded, according to Hamas and the army, further straining Egyptian efforts to mediate a cease-fire. Throughout the fighting, Palestinians fired rockets and mortar shells toward southern Israel, Israel's army said, though no civilian casualties were reported.

The soldiers were killed after troops spotted two Hamas militants planting a bomb near the Israeli border. Troops pursued the militants, only to fall into an ambush by another Hamas force lying in wait, Israeli defense officials said.

The officials, who spoke on condition of anonymity because the investigation was still ongoing, said the attack wasn't expected to lead to an escalation in Israel's military policy of targeting militants with pinpoint airstrikes and raids.

The Israeli soldiers were killed near the Nahal Oz terminal used by Israel to pump fuel into Gaza. The fuel supply was cut off last week after two Israeli civilians were killed in a Palestinian attack on the terminal - the only source of fuel for Gaza. Fuel shipments were to be resumed Wednesday.

"We were supposed to resupply the fuel beginning today," said army spokeswoman Maj. Avital Leibovich. "We didn't because of this event in this area. ... At this point the supply will not be renewed today."

It was not immediately clear when fuel deliveries would resume. Palestinians say the Israeli sanctions have caused widespread hardship in Gaza. On Tuesday, the United Nations said it was gravely concerned about the effects of the fuel cutbacks.

Israel has been cutting back on fuel and other basic supplies allowed into Gaza for months, trying to pressure Gaza's Islamic Hamas government to stop rocket attacks.

After Wednesday's clash, Hamas warned Israeli soldiers that they would face death, injury, kidnapping or "psychological trouble" if they raid the Gaza Strip.

"This is a letter to the Zionist enemy," Hamas spokesman Abu Obeida said. "We will be the flaming rock upon which you will fall."

During the fighting near Nahal Oz, two Palestinian civilians were injured when their house was hit by a tank shell in the area, medics said. The army did not comment.

In a separate incident, Israeli troops entered northern Gaza early Wednesday in what the military spokesman said was a "routine operation" to target militants launching rockets.

Troops identified hitting gunmen at several points, the army said. Israeli aircraft also fired at a group of gunmen, the army said. Hamas said four of its fighters were killed and three wounded. Health officials said a 42-year-old farmer was shot and wounded.

Israeli armored vehicles hit and damaged a mosque, destroyed two houses and partially demolished one other, local residents said. The army said the mosque was full of explosives and exploded during an exchange of fire between troops and gunmen located inside. The troops withdrew from there at daybreak.

Israel's army frequently raids the Gaza Strip or launches air strikes to target militant squads that launch rockets at Israel almost daily. The crude rockets wreak panic on southern Israel and occasionally cause casualties.

Hamas, a violent group committed to Israel's destruction, seized control of Gaza last June. Its continued control of the area, along with the near-daily fighting with Israel, has jeopardized Mideast peace efforts.

Israel hopes to reach a peace agreement with the moderate West Bank government of Palestinian President Mahmoud Abbas by the end of the year. But it says it will not carry out any accord until Abbas regains control of Gaza.