Egypt's security forces were on high alert Monday ahead of pro-democracy protests to mark the second anniversary of former president Hosni Mubarak's ouster, a police official told AFP.
Authorities have boosted security around the presidential palace, the interior ministry and around Cairo's Tahrir Square, as well as around key public installations, the official said.
Marches were due to set off at 5:00 pm (1500 GMT) towards Tahrir -- epicentre of protests that toppled Mubarak -- and the presidential palace where violent protests have been staged against Islamist President Mohamed Morsi.
"There will also be extra security around the main metro stations after some groups threatened to block the tracks," the official said.
Protesters briefly blocked trains in a central Cairo metro station, scuffling with passengers and metro police, and a major bridge, witnesses and state media reported.
Opposition parties and movements have called for a day of action, demanding Morsi fulfill the goals of the revolution that brought him and his long-banned movement, the Muslim Brotherhood, to power.
Two years ago, Egyptians poured into the streets to celebrate Mubarak's ouster, buoyant that democratic change was possible.
The 84-year-old's spectacular fall from grace in a popular revolt sent shock waves across the Middle East and beyond when he announced his resignation on February 11, 2011 after an 18-day popular revolt.
But two years later, many are angry that the main goals of the revolt -- freedom and social justice -- have not been achieved and that Egypt is more polarised between Morsi's mainly Islamist supporters and a broad opposition.
Among the key demands of Monday's protests are a new unity government, amendments to a controversial Islamist-drafted constitution and the sacking of the prosecutor general.
Egypt has witnessed deadly violence, insecurity and price hikes, fuelling the political turmoil gripping the country.