A helicopter crash in the restive Sinai Peninsula killed five Egyptian soldiers on Saturday, medics said.

The military confirmed a helicopter had crashed and said a search was under way for its crew.

Kidnappers seized Egypt's cultural attache and three other embassy staff in the Libyan capital on Saturday a day after a group snatched another Egyptian official in the city.

Meanwhile, the toll from clashes in the south and west rose to 154 dead and 463 wounded, a further sign of the chronic instability that has plagued Libya since the 2011 uprising ousted dictator Moammar Gadhafi.

An al-Qaida inspired group in Egypt claimed responsibility on Saturday for four bombings targeting police in Cairo that killed six people the day before.

Ansar Beit al-Maqdis, or Partisans of Jerusalem, also called in its statement for Muslims to stay away from police buildings.

Centuries-old glass and porcelain pieces were smashed to powder, a priceless wooden prayer niche was destroyed and manuscripts were soaked by water spewing from broken pipes when a car bombing wreaked havoc on Cairo's renowned Islamic Art Museum.

Experts scrambled to try to save thousands of priceless treasures as ceilings crumbled in the 19th-century building, which had just undergone a multimillion-dollar renovation.

An assailant threw a small bomb at a Cairo police building Saturday, police said, as rival demonstrators prepared to commemorate the 2011 uprising and a day after a spate of deadly bombings.

The small "incendiary bomb" lodged on the wall of the police training center and exploded without causing any casualties, a police official said.

Kidnappers seized an Egyptian diplomat in the Libyan capital Tripoli on Friday, Libya's foreign ministry said.

The diplomat was snatched from his house in Tripoli by an unknown group, Libyan foreign ministry spokesman Said Lassoued told Agence France Presse.

The United States "strongly" condemned Friday's bombings in Egypt and appealed for calm on the eve of the third anniversary of the Egyptian revolution.

Washington has been walking on eggshells for three years with its key ally in the Arab world, and it froze part of its military aid after Islamist president Mohammed Morsi was overthrown.

Two journalists and a driver working for German public television were attacked by a crowd in Cairo Friday as they covered a car bomb that struck the police headquarters in the Egyptian capital, the broadcaster said.

The angry mob set upon the three -- a cameraman, producer and driver -- branding them "traitors" and "lackeys of the Muslim Brotherhood," broadcaster ARD said on its website.

Three years after being hailed as heroes for toppling Egypt's Hosni Mubarak, the young activists who led the 2011 uprising say an even more repressive regime has emerged.

Their revolt captivated the world and galvanized the Arab Spring, raising hopes that long-ruling dictators across the region would be swept aside by popular demands for democratic change.

A suicide car bomber struck Cairo police headquarters Friday, the first of four blasts in Egypt's capital that killed six people on the eve of the anniversary of the 2011 uprising.

The bombings, all targeting the police, came as street clashes between Islamist supporters of deposed president Mohammed Morsi and backers of the military killed eight people, a day before planned rallies to mark the revolt that drove Hosni Mubarak from power.