Jerusalem ? Israel attacked Yasser Arafat’s Gaza office by air and sea, killing four guards early today, a day after violence by both sides left 15 dead in one of the bloodiest periods of the Palestinian uprising.

In a separate raid early today, Israeli tanks shelled two Palestinian police outposts in the West Bank town of Nablus, killing five policemen, Palestinians said. The Israeli military said only that there was military activity in the area.

As Israeli warships fired machine guns and a missile at Arafat’s office, killing the guards, Israeli helicopters sent missiles into nearby police compounds and a warplane dropped a bomb.

The attacks in Gaza, which began at 3 a.m., were still in progress three hours later, witnesses said, adding there were at least 40 explosions.

It was the first time that the Israeli military targeted Arafat’s headquarters in Gaza. Arafat was at his West Bank headquarters, trapped there by Israeli tanks.

Palestinians in nearby buildings fled in panic. “This is another night of terror,” said Ilham Johfur, who was fleeing with her two small children in tow. They joined hundreds in the streets, fearing their buildings would be hit. About 65 people went to hospitals suffering from shock, doctors said.

The latest Israeli strikes capped one of the most violent days in the 17-month Israeli-Palestinian conflict.

Palestinian gunmen late Tuesday infiltrated an army post near Ein Arik on the West Bank, killing six Israeli soldiers, the Israeli army said. The Al Aqsa Brigades, linked to Arafat’s Fatah, claimed responsibility.

Earlier Israeli airstrikes along with shelling and a raid by undercover forces left eight Palestinians dead, according to Palestinian sources.

Tuesday began with a Palestinian suicide bomber blowing himself up seconds after he was pushed off an Israeli bus by its suspicious driver in the West Bank, police said.

The upsurge in violence increased the pressure on Prime Minister Ariel Sharon to take more decisive action.

Deputy Internal Security Minister Gideon Ezra said the Palestinians had taken over the element of surprise, once an Israeli prerogative.

“They attack and we defend. In the past we attacked and they defended,” Ezra said. “We need to return to that … we have to control the situation.”

A group of 1,200 retired Israeli security officials proposed an immediate Israeli withdrawal from much of the West Bank and Gaza Strip, and the dismantling of 40 to 50 isolated Jewish settlements.