CAIRO (AP) — Egyptians delivered an angry backlash against President Mohammed Morsi and his Muslim Brotherhood on Friday, marking the second anniversary of the start of the country's revolution with tens of thousands filling major squares and streets around the country to call for a new regime change.

Two years to the day that protesters first rose up against now-toppled autocrat Hosni Mubarak, Egypt is entrenched in the new phase of its upheaval — the struggle between ruling Islamists and their opponents, played out on the backdrop of a worsening economy.

Rallies turned to clashes near Tahrir Square and outside the presidential palace in Cairo and in multiple cities around the country, with police firing tear gas and protesters throwing stones. At least four people, including a 14-year-old boy, were killed in the day's worst clashes, in the city of Suez, where protesters set ablaze a building that once housed the city's local government.

More than 370 were injured nationwide, the Health Ministry said, including five in Suez with gunshot wounds, raising the possibility of a higher death toll, the state news agency said.

Friday's rallies appeared to have brought out at least 500,000 opposition supporters, a small proportion of Egypt's 85 million people, but large enough to suggest that opposition to Morsi and his Islamist allies is strong in a country fatigued by two years of political turmoil, surging crime and a free falling economy that is fueling popular anger. Protests — and clashes — took place in at least 12 of Egypt's 27 provinces, including several that are Islamist strongholds.

"After what happened to me, I will never leave until Morsi leaves," said protester Sara Mohammed after she was treated for tear gas inhalation during clashes outside the president's palace in Cairo's Heliopolis district. "What can possibly happen to us? Will we die? That's fine, because then I will be with God as a martyr. Many have died before us and even if we don't see change, future generations will."

The immediate goal of the opposition was to have a show of strength to push Morsi to amend the country's new constitution, which was pushed through by his Islamist allies and rushed through a national referendum last month.

But more broadly, protesters are trying to show the extent of public anger against the Muslim Brotherhood, the organization Morsi hails from, which they say is acting unilaterally and taking over the state rather than setting up a broad-based democracy.

Morsi is Egypt's first freely elected and civilian president, a significant feat given that all his four predecessors were of military background. But his six months in office have been marred by some of the worst crises since Mubarak's ouster and divisions that have left the nation scarred and in disarray. A giant wave of demonstrations erupted in November and December following a series of presidential decrees, since rescinded, that gave Morsi near absolute powers, placing him above any oversight, including by the judiciary.

The Brotherhood and its Islamist allies, including the ultraconservative Salafis, have justified their hold by pointing to their string of election victories the past year — though the opposition says they have gone far beyond what in many ways is a narrow mandate — Morsi won the presidency with less than 52 percent of the vote. Brotherhood officials have increasingly depicted the opposition as undemocratic, trying to use the streets to overturn an elected leadership.

Thursday night, Morsi gave a televised speech that showed the extent of the estrangement between the two sides. He denounced what he called a "counter-revolution" that is "being led by remnants of ousted president Hosni Mubarak's regime to obstruct everything in the country."

Unlike in 2012, when both sides made a show of marking Jan. 25 — though, granted, not together — the Brotherhood stayed off the streets for Friday's anniversary. The group said it was honoring the occasion with acts of public service, like treating the sick and planting trees.

On the horizon are key elections to choose a new lower house of parliament. The opposition is hoping it can leverage public anger into a substantial bloc in the legislature, but it is still trying to weld together an effective campaign coalition in the face of Islamists' strength at the ballot box. Last winter, the Brotherhood and Salafis won around 75 percent of the lower house's seats, though the body was later disbanded by court order.

Pending the election of a new lower house, Morsi gave legislative powers to parliament's Islamist-dominated upper house, a normally toothless chamber that only about seven percent of Egypt's 50 million eligible voters bothered to elect in balloting last year.

The violence Friday pointed to the increasing tempers among some in the opposition, particularly younger men who have been the most restive. Clashes erupted outside the presidential palace when youths tried to push through a police barricade outside the gates. In other cities, protesters tried to break into offices of the Brotherhood's political party or government and security buildings.

Beyond the violence, the protests re-created the tone of the 18-day uprising against Mubarak, including the same chants, this time directed against Morsi — "Erhal! Erhal!", Arabic for "leave, leave" and "the people want to topple the regime."

Some of the protesters are planning sit-in strikes in major squares and streets, insisting that they will not go home before Morsi leaves office.

Standing near Tahrir Square, retiree Ahmed Afifi declared that he joined Friday's protests because he was struggling to feed his five children on less than $200 a month.

"I am retired and took another job just to make ends meet," he said, his eyes tearing. "I am close to begging. Under Mubarak life was hard but at least we had security ... The first people hit by high prices are the poor people right here."

Tens of thousands massed in Cairo's Tahrir Square, where the 2011 uprising began, and outside Morsi's palace. Banners outside the palace proclaimed, "No to the corrupt Muslim Brotherhood government" and "Two years since the revolution, where is social justice?" Others demonstrated outside the state TV and radio building overlooking the Nile.

In two towns in the Nile Delta, Menouf and Shibeen el-Koum, protesters blocked railway lines, disrupting train services to and from Cairo. In Ismailia on the Suez Canal, protesters stormed the building housing the provincial government, looting some of its contents. There were also clashes outside Morsi's home in the Nile Delta province of Sharqiyah.

The demands of Friday's protesters vary. Some on the extremist fringe of Egypt's loosely knit opposition want Morsi to step down and the constitution adopted last month rescinded. Others are calling for the document to be amended and early presidential elections held.

"There must be a constitution for all Egyptians. A constitution that every one of us sees himself in it," opposition leader Mohamed ElBaradei said in a televised message posted on his party's website.

Egypt's bestselling novelist and democracy campaigner Alaa al-Aswany marched with ElBaradei on Friday to Tahrir. "It is impossible to impose a constitution on Egyptians, a constitution which was sponsored by the Supreme guide of the Muslim Brotherhood, and the revolution today will bring this constitution down," he said.

Protester Ehab Menyawi said he felt no personal animosity against the Brotherhood but opposed its approach toward Morsi as Egypt's first freely elected leader.

"The Brotherhood thinks that reform was achieved when their man came to power and that in itself is a guarantee for the end of corruption," he said as he marched from the upscale Cairo district of Mohandiseen to Tahrir with some 20,000 others.

Morsi has kept government policy-making and the choice of appointments almost entirely within the Brotherhood. Members and supporters of the group are being installed bit by bit throughout the state infrastructure — from governor posts, to chiefs of state TV and newspapers, down to preachers in state-run mosques.

Many were also angered by the constitution and the manner of its adoption. Islamists finalized the draft in a rushed, all-night meeting, throwing in amendments to fit their needs, then pushed it through a swift referendum in which only a third of voters participated. The result is a document that could bring a much stricter implementation of Shariah, or Islamic law, than modern Egypt has ever seen.

Looming over the struggle between the opposition against the Islamists is an economy that has been in tatters since Mubarak's ouster. The vital tourism sector has slumped, investment shriveled, foreign currency reserves have tumbled, prices are on the rise and the local currency has been sliding.

More pain is likely in the coming months if the government implements unpopular new austerity measures to secure a $4.8 billion loan from the International Monetary Fund.

"Egypt is in a bad place, It's been wholly consumed with issues of power, and governance has been left by the wayside. None of this had to be," said Michael W. Hanna, a senior fellow at the New York-based Century Foundation.

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Associated Press reporters Aya Batrawy and Mariam Rizk contributed to this report.