Egyptians poured out anger at Israel's mistaken killing of three border policemen protested after Friday prayers at Cairo's main mosque under a banner that read: "The pigs' apology doesn't quench our rage."

Israel's army chief promised a swift investigation.

About 600 people protested the killings after prayers at the millennium-old Al-Azhar (search) mosque, carrying banners: "Don't forget Oct. 6, 1973," the day Egypt (search) initiated its last war with Israel, and "The pigs' apology doesn't quench our rage."

Police in both riot gear and plainclothes kept a close watch on the crowd as speakers denounced the shooting and trouble elsewhere in the Middle East, chiefly the chaos in Iraq following the U.S.-led invasion.

Protesters echoed comments by Arab League Secretary-General Amr Moussa (search) on Thursday that the killing of the three Egyptians was "a new element added to the deteriorating situation in the region."

The Israeli army chief, Lt. Gen. Moshe Yaalon, told Israeli Army Radio Friday that the shooting occurred after a commander in the field identified a group of Palestinian militants and soldiers operating a tank shot in the wrong direction. The army will complete its investigation by next week and give the results to the Egyptians, Yaalon said.

In an official response to the border shooting that may have been meant as much for domestic as Israeli consumption, the Egyptian Foreign Ministry issued a formal protest and demanded an investigation. The ministry statement did not mention whether Israeli Prime Minister Ariel Sharon's apology, delivered in a call to Egyptian President Hosni Mubarak, had been accepted.

There was already widespread anger in Egypt at what is seen as Israel's heavy-handed response to the Palestinian uprising. Egyptian protesters periodically call on their government to tear up its 1979 peace treaty with Israel, the first between an Arab government and the Jewish state.

Egyptian editor Emad Gad, whose monthly Israeli Digest about Arab-Israeli affairs is seen as close to the government, said that despite the public outcry, the shooting would not escalate into a bilateral crisis.

Egyptian government officials, mindful of Egypt's role as a mediator in an Israeli plan to withdraw from Gaza, would ensure reaction to the shooting is "carefully guided," he said.

Israel's swift apology and pledge to investigate was derided in some Egyptian quarters Friday.

The liberal opposition daily Al-Wafd declared in a front-page headline that Egyptians "rejected" the apology. The independent Al Masri Al Youm said in an editorial: "An apology, no matter how many artificial words or how much grief it contains, doesn't heal an attack on the nations' honor."

Pro-government Al-Ahram carried interviews with relatives and friends of the three policemen — Amer Abu Bakr Amer, Hani Ali Sobhi al-Naggar and Mohammed Abdel Fattah.

Ezzat Ramadan, a friend of Amer's, was quoted as demanding trials of those responsible and saying: "All our village rejects the Israeli apology."

A special prayer was performed at noon Friday for the soldiers at a mosque near the Israeli border before their bodies were taken to be buried in their hometowns.

The shooting came at a particularly sensitive time in Israeli-Egyptian relations.

Egyptian Foreign Minister Ahmed Aboul Gheit was to travel to Israel next week to discuss Sharon's plan to withdrawn from the Gaza Strip. Egypt has been working with the Palestinians and the Israelis to try to ensure stability in Gaza, which is on its border. There are fears the recent death of Yasser Arafat will make volatile Gaza even harder to control.

A Foreign Ministry official said Thursday that Aboul Gheit still planned to make the trip.