Gaza City, Gaza Strip ? Israeli warplanes pummeled Hamas targets Friday in a stepped-up campaign against militants firing rockets into southern Israel, while Palestinian factions battled with automatic weapons and grenades at a Gaza university.

Street battles between Fatah and Hamas remained less intense than the heavy fighting that terrorized Gaza City two days earlier, but a truce agreement late Thursday enjoyed no more success than previous cease-fires declared this week.

With the political leaders of the factions seemingly not in control of their gunmen, Hamas militiamen raised the internal strife to an ominous new level by widening their targets beyond armed rivals and seizing aides to two Fatah officials.

The infighting that began Sunday has killed more than 50 Palestinians and wounded dozens, while the death toll from Israeli attacks rose to 20 as airstrikes killed eight people Friday.

Israeli missiles came screeching down at least five times in retaliation for Hamas rocket attacks that have panicked people in southern Israel. At least 13 more militant rockets fell, wounding four Israelis in the battered town of Sderot.

Despite the escalating air campaign, a senior Israeli army officer said there were no immediate plans for a major ground offensive against rocket teams, saying Israel was reluctant to do something that might unite the Palestinian factions. He spoke on condition of anonymity because no final decision had been made.

One airstrike incinerated a minivan carrying Hamas militants and what the Israeli army described as “a large amount of weapons.” Three fighters were killed and 12 people were wounded, Palestinian hospital officials said.

An earlier airstrike east of Gaza City killed five Palestinians, including at least three Hamas militants, and wounded six. Israel’s military said the target was a Hamas headquarters building.

Hamas said the Israeli military had called the home of Ahmed Jaabari, head of Hamas’ military wing, and warned his family the house would be hit. People gathered around the building to discourage an attack, he said. The Israeli military had no comment.

The latest bloodshed was touched off by Palestinian President Mahmoud Abbas of Fatah to deploy thousands of security officers in Gaza City last week to try to restore law and order. Hamas called that a provocation because it wasn’t consulted and fighting broke out Sunday.