Egypt's Muslim Brotherhood was holding a "day of anger" Thursday to mark the first anniversary of the military overthrow of president Mohamed Morsi, with police swiftly quashing the few marches that began.
The protests are being seen as a test of the Islamists' strength, with the Brotherhood-led Anti Coup Alliance having issued an aggressive rallying cry on Wednesday demanding a "day of anger" to mark Morsi's ouster.
Police closed off several main squares in Cairo and beefed up security ahead of the protests.
According to security officials, police quickly moved in on two marches, firing tear gas and dispersing the protesters.
An Islamist activist told AFP marches would be staggered throughout the day.
Police were also on high alert for further bombings, days after two senior policemen were killed when devices they were defusing outside the presidential palace exploded.
Morsi's Muslim Brotherhood movement was listed as a terrorist group after his overthrow on July 3 and many of its leaders, including Morsi himself, jailed.
The ex-army chief who toppled him, Abdel Fattah al-Sisi, has since replaced him as president.
Despite the crackdown, the Islamists have insisted on continuing their protests in the hope, they say, of making the country ungovernable for Sisi.
Since Morsi's ouster after a turbulent year in power, at least 1,400 people have been killed in street clashes, and more than 15,000 thousand have been imprisoned.
Among the Brotherhood leaders arrested was supreme guide Mohamed Badie, who was sentenced to death in a speedy mass trial.
Militants have launched scores of attacks that killed several hundred policemen and soldiers, mostly in the restive Sinai peninsula.
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Rights groups say the crackdown has been the bloodiest seen in Egypt in decades.
"A surge in arbitrary arrests, detentions and harrowing incidents of torture and deaths in police custody recorded by Amnesty International provide strong evidence of the sharp deterioration in human rights in Egypt in the year since President Mohamed Morsi was ousted," the London-based Amnesty said in a statement.
The repression has further divided Egypt, a regional powerhouse and the Arab world's most populous country, with a quickly growing population of 86 million stretching its dilapidated infrastructure.
The military had overthrown Morsi after days of huge protests demanding the resignation of the polarising Islamist. Almost 23 million voters went on to endorse Sisi in a May presidential election against a weak leftist candidate who garnered only several hundred thousand votes.
Sisi's supporters view him as a strong leader who can restore stability in the often tumultuous country.
Yet the Brotherhood, which had won every vote since an uprising toppled veteran strongman Hosni Mubarak in 2011, still commands a loyal following.
"Let us turn our wealth of revolutionary defiance into an overwhelming power," the Anti Coup Alliance said in its statement on Wednesday.
A man was killed overnight apparently preparing an explosive in an apartment south of Cairo, security officials said.
In Cairo, a small bomb went off inside a car near a military installation late Wednesday. Police arrested a man who was in the car, while another escaped.
The government says the Brotherhood has been behind the militant attacks, a charge the Islamist group denies.