CAIRO - A suicide car bomber blew himself up in the parking lot of a top security compound in central Cairo on Friday, killing at least four people in one of the most high-profile attacks on the state in months, security sources said.

The early morning explosion damaged the Cairo Security Directorate, which includes police and state security, and sent smoke rising over the capital, raising concerns that an Islamist insurgency was gathering pace.

Tensions were rising in other parts of Cairo, which has seen numerous protests and street violence since the army deposed Islamist president Mohamed Morsi in July after mass protests against his rule.

Fierce clashes broke out between Morsi supporters and security forces on the road leading to the Pyramids of Giza, where about 2,000 Islamists gathered. Some burned tyres and hurled petrol bombs at police, who responded by firing tear gas.

Clashes were also reported on Friday in Suez City, Ismailia and Alexandria.

Hours after the first bomb attack, the capital and its environs witnessed two smaller blasts.

A crude explosive device killed one policeman and wounded nine others in another Cairo neighborhood, the Interior Ministry said in a statement. Security sources said a person driving past security vehicles had hurled a hand grenade in their direction.

In Giza, a large district on the outskirts of Cairo, a third explosion went off near a police station. There were no immediate reports of casualties.

The dead from the first blast at the parking lot included three policemen, security sources said. State television quoted the Cairo governor as saying 50 people were wounded.

The attack also heavily damaged the nearby Islamic Art Museum, an official told the state news agency.

In a statement, the office of President Adly Mansour said it would "avenge the deaths of the martyears" who died at the Security Directorate and severely punish the perpetrators.

TURMOIL AND VIOLENCE

Reuters witnesses heard gunfire immediately after the blast, which twisted the metal and shattered windows of nearby shops. Wood and metal debris were scattered hundreds of metres around.

One body covered in a blanket lay in a pool of blood near a scorched car engine.

State television quoted witnesses as saying gunmen on motorcycles opened fire on buildings after the explosion.

There was no immediate claim of responsibility for the attack, which came a day before the third anniversary of the uprising that toppled autocrat Hosni Mubarak and raised hopes of a stable democracy in the Arab world's biggest nation.

Instead, relentless political turmoil has hit investment and tourism hard in Egypt, which has a peace treaty with neighboring Israel and controls the Suez Canal.

After ousting Morsi, army chief General Abdel Fattah al-Sisi unveiled a political road map he said would bring elections and calm to Egypt.

Security forces have killed hundreds of Brotherhood members and jailed thousands more, including top leaders.

The army-backed government has effectively removed the Brotherhood from politics and many Egyptians turned against it after Morsi's troubled one-year rule.

Intense pressure on the movement has severely hurt its ability to stage mass protests it had hoped would reverse what it calls an army coup that has undermined Egypt's democratic credentials.