Huge crowds took to the streets of Cairo Sunday to demand the resignation of President Mohamed Morsi.
The demonstrations -- the largest since the revolution that swept former president Hosni Mubarak from power -- were largely peaceful. However scattered violence after nightfall left at least one person dead and 40 injured as a crowd firebombed the Cairo headquarters of Mr. Morsi's Muslim Brotherhood.
Reuters news agency says at least three other Brotherhood offices were attacked in separate protests in the Nile delta.
Secular and liberal opponents of Mr. Morsi -- many of them waving Egyptian flags -- swarmed Cairo's Tahrir Square on Sunday, the first anniversary of his inauguration as Egypt's first freely elected leader. Arabic-language media quoted the Interior Ministry saying the crowds in Cairo and other cities across Egypt totalled as many as 3 million people.
Critics accuse the Morsi-led government of trying to monopolize power and of failing to fix the struggling Egyptian economy. Many have also voiced anger at Egypt's worsening crime and persistent political and religious violence.
Protesters chanted "leave" and "the people want the fall of the regime" -- an echo of the 2011 slogan that helped drive Mr. Mubarak from power and cleared the way for Mr. Morsi's 2012 election victory.
Earlier Sunday in the capital, Mr. Morsi's Islamist backers rallied around a mosque near the presidential palace, vowing to defend him against what they see as opposition efforts to oust a democratically elected leader. Morsi supporters also accuse the opposition of trying to return Egypt to the Mubarak era.
As tensions mounted, the Presidential office issued a statement saying dialogue is the only way out of Egypt's political crisis.
In an interview published Sunday in the British newspaper The Guardian, the president said that if he gave in to the pressure, a new president could face similar opposition demands to quit after a "week or a month."
Street battles linked to the political tension killed at least seven people in the past week, among them an American student stabbed to death while photographing protests in Alexandria.
U.S. Deputy National Security Adviser Ben Rhodes said the United States has boosted security at its embassy and consulates in Egypt. Speaking Sunday, he also said the Obama administration has been in touch with Egyptian government officials and opposition figures to urge them to resolve their differences peacefully.