Egyptian protesters clashed violently with police in cities across the country Friday as frustration with the elected Islamist government reached a new climax on the two year-year anniversary of the uprising that ousted Hosni Mubarak.

By Friday night, four people had been killed in the city of Suez and 379 injured around the country, the state news wire reported. The violence threatened to precipitate a fresh round of political turmoil a month after a conflict over Egypt’s new constitution stalled efforts to mend a shattered economy and carved a bitter rift between supporters of the ruling Islamists and their liberal opposition.

The scenes in Cairo’s Tahrir Square recalled earlier protests that have punctuated the months of turbulence since Mubarak’s ouster. During the day, activists hoisted banners and called for the downfall of the government — now under the leadership of President Mohamed Morsi, an Islamist backed by the powerful Muslim Brotherhood.

But nightfall saw the clashes grow more violent, as protesters hurled rocks and Molotov cocktails at police barricades and government buildings and were met by thundering barrages of tear-gas fire.

The protests underscored the deep national divide that has persisted since the ratification of a new, Islamist-backed constitution last month, which critics say provided for a stricter interpretation of Islamic law.

It also exposed the divergent tactics employed by the ascendant Islamists and their disparate opposition in the run-up to spring parliamentary elections.

As young men battled police on the edges of Tahrir Square and outside the state television building and the presidential palace on Friday, Morsi’s backers in the Muslim Brotherhood embarked on the third day of a nationwide charity initiative titled “Let’s Build Egypt,” involving tree planting, school construction and the provision of food and medical care to the poor.

“We think this is the best way to do what we can for our country. They have their thoughts, and we have ours,” said Haitham al-Melah, a Brotherhood member who was helping to run one of the group’s wholesale food markets in a poor Cairo neighborhood Friday. “Protesting accomplishes some work, but the actual work needs to be done in every field.”

The contrast in tactics also reflected sharply different expectations for the parliamentary vote. Many opposition protesters, embittered by last month’s battle over the religious character of the new constitution, said Friday that they have little hope for gain through the ballot box.

The month-long crisis saw Islamists square off against a diverse opposition of liberals, secularists and loyalists of the former government in protests and street battles that left 10 people dead.

The charter was ratified on Dec. 25 after it was approved in a national referendum. But lingering frustration over Islamist rule and a stagnant economy has continued to fuel heated, if divided, opposition.

Many other protesters said they joined Friday’s marches out of anger over rising food prices and an increasingly tight job market.

TIMELINE: Key events in Egypt since the fall of Hosni Mubarak.

“The goal is to bring down Morsi’s regime. Morsi has had a year in office so far, and nothing has been done,” said one protester, Abdel Hamid al-Khouli, an accountant. “People are suffering. Jobs have stopped. Food has stopped.”

Also at Tahrir Square were hundreds of al-Ahly club soccer fans, who called on the government to issue swift verdicts in the cases of those charged with killing fans in a deadly soccer riot last year.

Islamist groups called on their followers to stay away from the protests to prevent violent clashes. But some activists accused the group of firing birdshot at the demonstrations from surrounding buildings.

The Brotherhood said Friday night that opposition activists had ransacked one of the group’s Freedom and Justice party offices in Cairo and set fire to another in the coastal city of Ismailia.

Skirmishes also erupted outside Muslim Brotherhood offices in at least three other cities in northern Egypt and outside a courthouse in Alexandria where police officers have been on trial for killing protesters during the 2011 revolution.

Sharaf al-Hourani contributed to this report.