Tel Aviv/Gaza  - Israeli-Palestinian violence in and from the Gaza Strip showed no sign of letting up Saturday, as the Israel Air Force (IAF) attacked 40 targets in the salient, and artillery also opened fire, and militants in the enclave continued launching rockets at the Jewish state.

For the first time since the offensive began one week ago, Israeli guns positioned along the border opened up in the late afternoon in what could be an indication that the long-expected ground invasion is close.

The artillery barrage continued for several hours. It was unclear whether it was an artillery shell or an airstrike which hit a mosque in the north of the Strip in the late afternoon, killing 11 Palestinians and wounding 50 others, 24 of them seriously.

It was not the first mosque hit in the Israeli offensive; the Israeli military has said militant Palestinians used mosques as weapons depots and even as rocket-launching bases.

Military spokespeople in Tel Aviv however had no immediate comment on the strike on the mosque Saturday afternoon.

One of the IAF strikes in the early hours of the morning killed a top Hamas commander, the third high-ranking leader of the Islamist group to be killed in the eight days of the Israeli offensive.

Zakaria al-Jamal was hit when planes attacked the vehicle in which he was driving.

The Israeli military said in a statement that Jamal was a battalion commander in the Hamas military wing, and the head of the movement's rocket-launching squads in Gaza City.

Israel also attacked a car carrying another top Hamas commander, Muhammad Maaruf, and a companion in the early afternoon. Their fate was unclear.

Other targets hit in the IAF strikes included a college, which the military statement said had been used as a rocket-launching base, and the homes of two Hamas militants. One home had been used as a weapons depot and the other as a meeting place to plan attacks, the statement said.

Four Palestinians were also killed in a strike on Rafah, in the south, bringing the day's death toll to at least 19.

Reports from the Gaza Strip also said Israeli aircraft attacked two bridges in the centre of the salient, making movement between the south of the enclave and Gaza City, in the north, harder.

Witnesses said that during one of the IAF sorties over Gaza City, one F-16 aircraft drew the mathematical symbol of infinity in the sky.

The symbol, which looks like the figure "8," was taken to mean that the strikes would continue without let up.

Gaza militants, for their part, continued to launch rockets and mortar shells at Israel, with around 15 attacks, including six with long-range Grad missiles, reported.

One Grad hit a building in the port city of Ashdod, lightly injuring two people and causing damage to the building.

Another rocket fired earlier Saturday morning struck a house in the coastal city of Ashkelon, sparking a fire in the building's yard. No injuries were reported.

Israel launched its "Operation Cast Lead" one week ago, in response to a week of heavy rocket barrages on the Jewish state out of the Gaza Strip following the end of a nervous six-month truce between Israel and Hamas leaders in the salient.

Some 461 Palestinians have been killed in the hundreds of Israeli strikes, and around 2,300 wounded.

The approximately 450 Palestinian rockets and mortars launched since the start of the operation have resulted in four Israelis killed, three of them civilians, and dozens more wounded.

Although the United Nations Relief and Works Agency (UNRWA) has said that at least a quarter of the Palestinian casualties are civilian, exiled Hamas leader Khaled Mashaal said his organization's losses have been "minimal" and that "the resistance and its infrastructure are fine."

Mashaal warned that Israel that its soldiers would face "a dark fate" if Israel sent ground forces into the Strip. Israeli troops have been massing on the border of the Strip in what is seen as an indication that Israel might send tanks, infantry and other ground units into the salient in a second stage of the offensive.

"You, soldiers of the occupiers, have to realize that a dark fate of death, injury and captivity will wait for you" if Israel decides to invade the Gaza Strip," Mishaal said from Damascus.

Over 10,000 Arab-Israelis, meanwhile, demonstrated Saturday in the northern town of Sakhnin, protesting the Israeli operation. Some of the marchers waved Palestinian flags, and a few carried the green flag of Hamas. There were no reports of violence.

In Tel Aviv Saturday night about 1,000 people gathered in the city's main Rabin square to protest the Israeli offensive. A counter- demonstration took place nearby in support of the Israeli operation. (dpa)