Gunmen who attacked an Egyptian border guards checkpoint on Saturday killed 21 soldiers, a military official told Agence France Presse, raising a previous death toll of 15 troops.

The attackers used rocket-propelled grenades and heavy machineguns in the attack on the post in the desert area of El-Farafrah, 630 kilometers (390 miles) west of Cairo, security officials said.

Egyptian soldiers in north Sinai prevented an aid convoy of activists from reaching the Rafah border crossing with the embattled Palestinian Gaza Strip on Saturday, an Agence France Presse correspondent said.

An army officer at the Balloza checkpoint, one of many along the desert highway to Rafah, told an AFP correspondent that the security situation in the restive peninsula was too unstable to allow the convoy of 11 buses and 500 activists to pass.

Israel's Foreign Minister Avigdor Lieberman has slammed Turkey's handling of violent anti-Israeli protests in Ankara and Istanbul, in a diplomatic spat over the Jewish state's assault on Gaza.

Lieberman accused Turkey of not taking the "necessary preventative measures" to stop protests getting violent after people angered by the offensive in Gaza tried to storm Israeli embassy buildings.

Turkish Prime Minister Recep Tayyip Erdogan on Friday slammed Egypt's President Abdel Fattah al-Sisi as an illegitimate tyrant, saying that Cairo could not be relied upon to negotiate a ceasefire with Israel.

"Is Sisi a party (to a ceasefire)? Sisi is a tyrant himself," Erdogan told reporters.

A son of ousted Egyptian president Mohamed Morsi, who was sentenced to a year in prison for possession and use of hashish, was arrested early Friday at a train station south of Cairo, security officials said.

Abdullah Morsi, 19, who security officials said was on the run, was arrested while boarding a train heading to Upper Egypt. His arrest was also reported by the official MENA news agency.

Israel launched a ground operation in Gaza late Thursday on the 10th day of an offensive to stamp out rocket attacks from the Palestinian enclave, the Israeli army said, as the death toll in Gaza rose to at least 240 and efforts to reach an Egypt-mediated ceasefire collapsed.

"Following 10 days of Hamas attacks by land, air and sea, and after repeated rejections of offers to deescalate the situation, the Israel Defense Forces (army) has initiated a ground operation within the Gaza Strip," it said in a statement.

Egypt's President Abdel Fattah al-Sisi and Palestinian leader Mahmoud Abbas on Thursday mulled holding a donors conference to rebuild Gaza, the Egyptian presidency said.

Sisi and Abbas, who discussed ways to end the Israeli offensive on the Palestinian enclave, also agreed that Israeli crossings to the besieged Gaza be opened to facilitate movement of people and goods.

French Foreign Minister Laurent Fabius will travel on Friday to Egypt and Israel for talks aimed at bringing the deadly conflict between the Israelis and Palestinians to an end, President Francois Hollande said Thursday.

Fabius said on Wednesday that Europe was ready to take action to help bring about a ceasefire between the two parties.

After proposing a stillborn truce denying Hamas any gains from its conflict with Israel, Egypt has had to negotiate with the Palestinian militants to halt the war on its doorstep, analysts said.

The initial truce was to have taken effect on Tuesday, apparently coordinated with Israel while bypassing Hamas.

Hamas demanded changes Wednesday to an Egyptian proposal to end the deadly conflict with Israel in and around Gaza, a Palestinian official said.

Hamas's demand came as the Palestinian death toll from Israel's punishing air campaign, now in its ninth day, rose to 220 Palestinians dead after the Islamist movement snubbed the truce plan on Tuesday even though it was briefly respected by Israel.