CAIRO, Nov 18: Cairo lodged a formal protest on Thursday after the Israeli army killed three Egyptian border policemen by mistake, threatening to plunge their delicate diplomatic ties into crisis mode.

Israeli Prime Minister Ariel Sharon sought to defuse the row by personally calling President Hosni Mubarak to express "deep sorrow" over the incident on the Gaza border and promised to keep him abreast of an official investigation.

But the strength of Egyptian feeling over the killing was illustrated by a statement from Foreign Minister Ahmed Abu Gheit, which said Cairo "strongly protested and condemned" the killings and called on Egypt's charge d'affaires in Tel Aviv to make a formal protest to the Israeli government.

"Egypt, which condemns and protests this regrettable incident, calls on the Israeli authorities to carry out a swift and comprehensive enquiry into the circumstances that led to this incident," Abu Gheit added.

"The dangerous nature of such events demands a very large degree of responsibility from the Israeli government for avoiding and preventing them from happening again."

Military sources in Israel said a tank unit had begun shelling after spotting what were believed to be three Palestinian militants trying to lay explosives along the border in the Rafah region of the southern Gaza Strip.

"An IDF (army) force opened fire towards the suspicious figures, but did not identify hitting them," the army said in a statement.

"Following an initial inquiry into the incident, it appears that there were operational and professional errors that occurred due to a misidentification of the three figures, which resulted in three Egyptian policemen being hit."

An Egyptian police report said the shelling was followed by "indiscriminate firing from Israeli soldiers towards the area where the shell fell."

Two policemen died instantly and the third on his way to hospital, police said. The dead were named as Hani Ali Sobhi el-Naggar, 21, Mohammed Abdul Fattah, 22, and Amr Abu Bakr Amr, 22. All three were doing their military service in the police.

A statement from Sharon's office said the prime minister had telephoned Mubarak and "expressed his deep sorrow over the regrettable incident."

"The prime minister said that this was a mishap and promised that the IDF (army) would investigate the incident and share its findings with Egypt. The prime minister added that Israel is ready to assist Egypt in accordance with any Egyptian request."

Egypt is one of the few Arab countries to have formal relations with Israel although ties have been at best lukewarm ever since their 1979 peace treaty.

The shooting comes at a particularly delicate time as the two countries have been coordinating closely ahead of Israel's planned pullout of troops and settlers from Gaza next year. Both governments have a desire to ensure that the territory does not become a stronghold for radical Islamist groups.

Israel agreed last month to let Egypt step up its military presence along the Rafah border while the government in Cairo has also offered to help train Palestinian police ahead of the withdrawal.

Abul Gheit and intelligence services chief Omar Suleiman are due to visit Israel next Wednesday. It was not clear whether the visit would still go ahead.

Rafah has seen some of the deadliest fighting of the Israeli-Palestinian conflict and militants regularly try to plant explosive devices along the border.

Israel has regularly accused Egypt of failing to put a halt to the smuggling of weapons under the border and has demolished a large number of cross border tunnels on the Gaza side of the frontier.

A number of Palestinians were buried alive Thursday when one of the tunnels collapsed. Israeli sources said its troops were helping recover the bodies after a request by Palestinian authorities although there was no immediate confirmation of how many people had died.-AFP