More than a thousand Egyptian demonstrators rallied in central Cairo on Friday demanding "the fall of the regime", in the largest protest challenging the government in two years.
By evening, after most protesters had left, police fired tear gas to disperse the remaining few, while plainclothes officers chased them down side streets to make arrests.
Police had earlier dispersed another rally elsewhere in Cairo and arrested at least 12 people.
The main protest, organised by leftist and secular activists, was ostensibly against a deal by President Abdel Fattah al-Sisi to hand over two islands to Saudi Arabia, during a visit by King Salman last week.
But pent-up frustrations over what activists call the president's heavy handedness and his style of governance dominated their chants.
"The people demand the fall of the regime," they chanted outside the journalists' syndicate in downtown Cairo.
That slogan was the signature chant of the Arab Spring uprisings in 2011, which led to the ouster of veteran Egyptian president Hosni Mubarak.
The protest on Friday was far smaller than those that filled Cairo's streets in 2011, and again in 2013 when millions rallied to demand Islamist president Mohamed Morsi's ouster by the military, then led by Sisi.
But a crackdown since Morsi's overthrow on protests that has killed more than 1,000 of his Islamist supporters has stifled demonstrations, which are now illegal without prior police permission.
Rallies by Morsi supporters, often met by swift police force, had waned since early 2014.
His Muslim Brotherhood movement has been banned as a terrorist group and thousands of its members, including Morsi, have been imprisoned.
The crackdown has spread to secular and leftist dissidents who had supported Morsi's overthrow and then turned on Sisi.
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- Dashing of hopes -
"The presence of this large number of protesters isn't just because of the islands," said Khaled Dawud, a prominent liberal activist and writer.
During a visit by King Salman last week, which brought Egypt billions of dollars in investments, the Egyptian government announced it was returning two islands in the Red Sea to Saudi Arabia.
It said the islands in the Straits of Tiran had been leased by Saudi Arabia to Egypt in 1950.
The announcement caused a storm of controversy in Egypt, with critics accusing Sisi of "selling" the islands.
Others who conceded they were Saudi to begin with criticised his government for announcing the deal only after it was signed.
The protesters on Friday included a gallery of prominent leftwing and liberal dissidents.
"There is an accumulation of things, and the dashing of the hopes we protested for on January 25," said Dawud, referring to the date when the anti-Mubarak revolt began.
The interior ministry had on Thursday warned against the protests and reminded Egyptians in a statement that unapproved demonstrations were illegal.
"What is significant is there is this number of protesters despite the interior ministry warning," Dawud said.
While Sisi, who won elections in 2014, is reviled by Islamists and secular dissidents, he is supported by many Egyptians say they need a strong leader to revive the economy after years of unrest.
He had enjoyed unwavering loyalty in much of the Egyptian media since he took office, but criticism of the president and his police force has grown in recent months.