Muslim protests against insults to the Prophet Mohammad turned violent in Pakistan, where at least 15 people were killed on Friday, the Muslim day of prayer, but remained mostly peaceful in other Islamic countries.
In France, where the publication of cartoons denigrating the Prophet stoked anger over an anti-Islam video made in California, authorities banned all protests over the issue.
"There will be strictly no exceptions. Demonstrations will be banned and broken up," said Interior Minister Manuel Valls.
Tunisia's Islamist-led government also banned protests against the images published by French satirical weekly Charlie Hebdo. Four people were killed and almost 30 wounded last week when the U.S. embassy was stormed in a protest over the film.
Many Western and Muslim politicians and clerics have appealed for calm, denouncing those behind the mockery of the Prophet, but also condemning violent reactions to it.
At street level, Muslims enraged by attacks on their faith spoke of a culture war against those in the West who put rights to freedom of expression before religious sensitivities.
"They hate him (the Prophet Mohammad) and show this through their continued works in the West, through their writings, cartoons, films and the way they launch war against him in schools," said Abdessalam Abdullah, a preacher at a mosque in Beirut's Palestinian refugee camp of Bourj al-Barajneh.
Muslims consider any depiction of the Prophet blasphemous.
Western diplomatic missions in Muslim nations tightened security ahead of Friday prayers. France ordered embassies, schools and cultural centres to close in a score of countries and Foreign Minister Laurent Fabius said some would stay shut over the weekend.
In Pakistan, tens of thousands of people joined protests encouraged by the government in several cities including Islamabad, Karachi, Peshawar, Lahore, Multan and Muzaffarabad.
The bloodiest unrest erupted in the southern city of Karachi, where 10 people were killed, including three policemen, and more than 100 wounded, according to Allah Bachayo Memon, spokesman of the chief minister of Sindh province. He said about 20 vehicles, three banks and five cinemas were set on fire.
Crowds set two cinemas ablaze and ransacked shops in the northwestern city of Peshawar, clashing with riot police who fired tear gas. At least five people were killed.
In Mardan in the northwest, police said a Christian church was set on fire and several people hurt.
Mohammed Tariq Khan, a protester in Islamabad, said: "Our demand is that whoever has blasphemed against our holy Prophet should be handed over to us so we can cut him up into tiny pieces in front of the entire nation."
Security forces fired in the air in Peshawar and the eastern city of Lahore to keep protesters away from U.S. consulates. Police fired tear gas at about 1,000 protesters in Islamabad.
The U.S. embassy in Pakistan has run television spots, one featuring Secretary of State Hillary Clinton, saying the government had nothing to do with the film about Mohammad.
Pakistan had declared Friday a "Day of Love" for the Prophet and Prime Minister Raja Pervez Ashraf said an attack on Islam's founder was "an attack on the whole 1.5 billion Muslims".
The Foreign Ministry summoned the U.S. chargÃ© d'affaires to lodge a protest over the video posted on YouTube, the latest in an array of irritants poisoning U.S.-Pakistani relations.
In neighbouring Afghanistan, police contacted religious and community leaders to try to prevent bloodshed. Protests in Kabul and the northern city of Mazar-e-Sharif only attracted a few hundred people and no violence was reported, but a cleric told one crowd: "If you kill Americans, it's legal and allowable."
About 10,000 Islamists gathered in the Bangladeshi capital Dhaka after Friday prayers, chanting slogans and burning U.S. and French flags and an effigy of U.S. President Barack Obama.
Protests went off peacefully in the Arab world, where last week several embassies were attacked and the U.S. envoy to Libya was killed in an initial burst of unrest over the film.
Thousands of Libyans marched in Benghazi on Friday in support of democracy and against the Islamist militias that Washington blames for the attack on the U.S. consulate last week that killed four Americans including the ambassador. Authorities said eight people in total had been arrested over the attack.
A few dozen Egyptians protested near the French embassy in Cairo, but were kept away from the premises by police deployed in large numbers to avoid a repeat of violence at the U.S. embassy last week.
Mainstream Islamic leaders in Egypt, where Islamist parties have moved to the heart of government since Hosni Mubarak was toppled, have expressed outrage, but urged a peaceful response.
In remarks to Reuters, the leader of the Nour Party, one of the biggest ultraorthodox Islamist parties in Egypt, echoed calls for the criminalisation of insults to religions including Islam. But he said it was important to separate between an offender and an entire society.
"The reasonable people in the West outnumber the thoughtless," said Emad Abdel Ghafour. "Contact should be kept up with the reasonable people," he added. "It is unreasonable that reactions come through arson and killing. We all suffer and are affected by these acts," he said.
In Yemen, where the U.S. embassy was stormed last week, several hundred Shi'ite protesters chanted anti-American slogans, but riot police blocked the route to the embassy.
Anger over the film brought several thousand Shi'ites and Sunnis together in a rare show of sectarian unity in Iraq's southern city of Basra, where they burnt U.S. and Israeli flags.
Thousands marched against the film on Thursday in a district of eastern Saudi Arabia where members of the Shi'ite Muslim minority have staged anti-government demonstrations since last year, a local activist said. Photographs of the march showed protesters burning American flags.
Lebanon's Hezbollah-run al-Manar television showed thousands of people waving Lebanese and yellow Hezbollah flags as they marched past the Roman ruins of Baalbek and shouted slogans such as "Death to America, death to those who insult the Prophet".
"Both the film and the cartoons are malicious and deliberately provocative. The film particularly portrays a disgracefully distorted image of Muslims," Rupert Colville, spokesman for U.N. High Commissioner for Human Rights Navi Pillay, told a news briefing in Geneva.
He said Pillay upheld people's right to protest peacefully, but saw no justification for violent and destructive reactions.
"In the case of Charlie Hebdo, given that they knew perfectly what happened in response to the film last week, it seems doubly irresponsible on their part to have published these cartoons," Colville said of the French magazine.