CAIRO/BEIRUT: Muslims angered by cartoons mocking the Prophet Mohammad should follow his example of enduring insults without retaliating, Egypt’s highest Islamic legal official said Thursday.

Western embassies tightened security in Sanaa, Yemen, fearing the cartoons published in a French magazine Wednesday could lead to more unrest in the Yemeni capital where crowds attacked the U.S. mission last week over an anti-Islam film made in America.

In the latest of a wave of protests against that video in the Islamic world, several thousand Shiite Muslims demonstrated in the northern Nigerian town of Zaria, burning an effigy of U.S. President Barack Obama and crying “Death to America.”

In the Pakistani capital, Islamabad, clashes between police and demonstrators injured at least 50 people.

The cartoons in France’s Charlie Hebdo satirical weekly have provoked little street anger so far, although about 100 Iranians demonstrated outside the French Embassy in Tehran.

In Tunisia, the birthplace of the Arab Spring revolts, the Islamist-led government decreed a ban on protests planned Friday against the cartoons.

Four people died and almost 30 others were wounded last week when protesters incensed by the movie about Prophet Mohammad stormed the U.S. Embassy.

An Islamist activist called for attacks in France to avenge the insult to Islam by the “slaves of the cross.”

Mu’awiyya al-Qahtani said on a website used by Islamist militants and monitored by SITE intelligence group: “Is there someone who will roll up his sleeves and bring back to us the glory of the hero Mohammed Merah?”

He was referring to an Al-Qaeda-inspired gunman who killed seven people, including three Jewish children, in the southern French city of Toulouse in March.

Condemning the publication of the cartoons in France as an act verging on incitement, Egypt’s Grand Mufti Ali Gomaa said it showed how polarized the West and the Muslim world had become.

Gomaa said Mohammad and his companions had endured “the worst insults from the non-believers of his time. Not only was his message routinely rejected, but he was often chased out of town, cursed and physically assaulted on numerous occasions.

“But his example was always to endure all personal insults and attacks without retaliation of any sort. There is no doubt that, since the Prophet is our greatest example in this life, this should also be the reaction of all Muslims.”

His statement echoed one by Al-Azhar, Egypt’s prestigious seat of Sunni learning, which condemned the caricatures showing the Prophet naked but said any protest should be peaceful.

The Coptic Orthodox Church in Egypt, whose population of 83 million people is 10 percent Christian, also condemned the cartoons as insults to Islam.

Gomaa said insults to Islam and the response, including the killing of the U.S. ambassador in Libya and attacks on other Western embassies in the region, could not be dissociated from other points of conflict between the West and the Muslim world.

He cited the treatment of Muslims at the U.S. detention center in Guantanamo, the U.S.-led war in Iraq, drone attacks in Yemen and Pakistan, and the demonization of Muslims by far-right European parties as “underlying factors” for the tensions.

After Friday’s invasion of the U.S. Embassy in Tunis, the Tunisian Interior Ministry has banned protests against the cartoon planned for Friday “to prevent human and material losses.” It warned that a state of emergency was still in force and that law “will be rigorously applied.”

The European Union issued a joint appeal, through its foreign policy chief, with the Arab League, African Union and Organization of Islamic Cooperation for “peace and tolerance.”

“We condemn any advocacy of religious hatred that constitutes incitement to hostility and violence,” the statement said.

“While fully recognizing freedom of expression, we believe in the importance of respecting all prophets, regardless of which religion they belong to.”

Despite the calls for calm, demonstrations turned violent in Pakistan’s capital Islamabad Thursday when thousands of protesters clashed with police close to Islamabad’s diplomatic enclave, leaving at least 50 people injured.

There have been dozens of demonstrations in Pakistan over the past week and the U.S. State Department has spent $70,000 to air adverts in Urdu across Pakistani television in a bid to disassociate the U.S. government from the inflammatory film, spokeswoman Victoria Nuland said.

There have been questions among lawmakers about whether the United States should continue aid to some countries, including Egypt, following the protests.

In Libya, where militias that helped overthrow Moammar Gadhafi still wield much power, the foreign minister offered an apology for U.S. ambassador Christopher Stevens’ death.

Secretary of State Hillary Clinton said Thursday she was forming a panel to investigate the attack, which the White House said bears the hallmarks of a “terrorist attack,” possibly linked to Al-Qaeda.

“It is self-evident that what happened in Benghazi was a terrorist attack,” White House spokesman Jay Carney told reporters traveling with President Barack Obama. “Our embassy was attacked violently and the result was four deaths of American officials.”

In recent days, Obama administration officials have slightly softened their claim that the attack was not preplanned, saying that while there is no intelligence to suggest it was, not all the facts are known.