JERUSALEM: A rocket fired by Gaza militants slammed into southern Israel on Saturday night for the second time in less than 36 hours, causing damages but no casualties, the military said.

"The rocket exploded near the town of Sderot (southern Israel), damaging a university building," an army spokeswoman said. No one was hurt.

On Friday Gaza militants fired a rocket that slammed into the southern Israeli city of Ashkelon, which also caused no casualties but some damage.

Israel responded with airstrikes on the Hamas-ruled Gaza Strip which killed a senior militant and wounded eight other people.

Hamas vowed revenge on Saturday for the overnight Israeli raids which the military wing of the Islamist group said killed Issa al-Batran, 40, who they identified as a senior field commander.

Hamas said the militant was killed when a raid struck a caravan near the Magazhi refugee camp in the centre of the Palestinian enclave. The Israeli military said the site was "a weapons-manufacturing warehouse."

"These new Zionist crimes will not pass without answer," Hamas said in a statement.

Israel has tried to kill Batran in the past. His wife and five sons were killed in an attack on his house during Israel`s three-week offensive on the territory in December 2008.

Overnight aircraft also fired at least four missiles at buildings used by Hamas security forces in Gaza City, wounding eight people, several of them seriously, the head of Gaza emergency services Muawiya Hassanein said.

The site targeted used to house the offices of Palestinian president Mahmud Abbas before his Western-backed Fatah party was ousted from Gaza by the Islamist Hamas in 2007.

Fearing further strikes, Hamas ordered the evacuation of all its security offices, a security source told AFP.

Warplanes also hit smuggling tunnels on the border with Egypt without causing casualties, witnesses said.

The rocket fired by Gaza militants on Friday prompted sharp criticism from the United Nations which said that "indiscriminate rocket fire against civilians is completely unacceptable and constitutes a terrorist attack."

The 122 mm Katyusha-type rocket landed next to a high-rise apartment building, damaging parked cars and shattering windows, the military said.

The Israeli military routinely responds after rocket attacks from Gaza, and the army said in a statement that it "holds Hamas solely responsible for terror emanating from the Gaza Strip."

Just over 100 rockets and mortar rounds have been fired from Gaza at southern Israel this year, compared with a daily barrage before the war, but most have not had the range to reach Ashkelon, 10 kilometres (six miles) north of Gaza.

BDST: 0913 HRS, August 01, 2010