* Three die in clashes with security forces, two in blast
* Limited Islamist protests in Cairo
* July 3 marks first anniversary of Islamist Mursi's ouster (Adds arrests, deaths at security operation in North Sinai)
By Shadia Nasralla
CAIRO, July 3 (Reuters) - Five people died in a bomb blast and clashes that broke out between security forces and protesters on Thursday marking the first anniversary of the army's ouster of elected Islamist President Mohamed Mursi.
Thousands of Egyptians opposed to the army's overthrow of Mursi joined protests in Cairo, witnesses said, but most of the gatherings attracted only dozens, were confined to narrow back streets and quickly dispersed amid tight security.
Armoured personnel carriers blocked off Cairo's Tahrir Square to prevent demonstrators from converging on the central spot, the symbolic heart of the 2011 uprising that ousted Hosni Mubarak after 30 years in power.
Thursday marked a year since President Abdel Fattah al-Sisi, then army chief, ousted the Muslim Brotherhood's Mursi following days of mass protests against his year-long rule.
In the weeks and months after the ouster, security forces launched a crackdown that saw thousands of Brotherhood members detained and hundreds killed. Egypt has since labelled the country's oldest Islamist movement a terrorist organisation.
Since Mursi's ouster, militant Islamist groups have launched a campaign of bombings and shootings targeting security forces in the sprawling capital.
The Muslim Brotherhood denies any link to the violence.
A call by Islamist opponents of Mursi's ouster for mass demonstrations appeared to fall flat on Thursday. It was not clear if more protests would take place after Iftar, the breaking of the fast during the Muslim holy month of Ramadan.
"On July 3, Egyptians will revolt, marking the beginning of the end of the coup, marching from all towns and cities across Egypt to liberty squares in all provinces," an alliance of Mursi's supporters said in a statement late on Wednesday.
Protests have petered out in Egypt in recent months as the crackdown has escalated, particularly since the government passed a law banning protests without prior police permission.
BOMBS AND CLASHES
Three of Thursday's victims died in clashes that broke out in Cairo between protesters and security forces, security sources said. The Interior Ministry said 150 Mursi supporters had been arrested at protests in several provinces.
Earlier in the day, two men died in a bomb blast at a flat in Kerdasa, a western district of the capital where around 10 policemen were killed by an Islamist mob last summer. Security sources said they believed one of the victims was involved in that police killing.
Another explosive device detonated on Thursday in a car in the northeastern district of Abbassiya and three home-made bombs went off near police cars in the central district of Imbaba without causing injuries, the sources added.
There were no immediate claims of responsibility.
Cairo has been hit by a spate of small explosions in recent days. Two police officers were killed on Monday trying to defuse bombs planted near the presidential palace.
Last week, a series of makeshift bombs also exploded at Cairo metro stations, the first such blasts in the capital since Sisi was sworn in as president last month.
State-news agency MENA reported that 17 militants were also killed in security operations in North Sinai, a hotbed of militant activity since before the 2011 uprising.
But Egypt's security dragnet has expanded over the past year to include secular and liberal activists, including many who played leading roles in a 2011 popular revolt against Mubarak.
Western governments and rights groups have voiced concern over freedom of expression in Egypt and the security clamp-down has dimmed hopes for democratic evolution that had soared after the anti-Mubarak uprising three years ago.
Amnesty International condemned Egypt's human rights record in a statement on Thursday, saying torture, arbitrary arrests and detentions had increased since Mursi's political demise.
"Egypt's notorious state security forces... are back and operating at full capacity, employing the same methods of torture and other ill-treatment used during the darkest hours of the Mubarak era," said Hassiba Hadj Sahraoui, deputy director of Amnesty's Middle East and North Africa programme.
Sisi's government says it is committed to a democratic transition and the rule of law following the 2011 uprising. (Additional reporting by Asma Alsharif and Lin Noueihed; Editing by Tom Heneghan)