In France, where the publication of cartoons denigrating the Prophet stoked anger over an anti-Islam video made in California, the authorities banned all protests over the issue on Friday.
"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 weekly Charlie Hebdo. Four people were killed and almost 30 were wounded last week when the US embassy was stormed in a protest over a film that mocked the Prophet.
Politicians and clerics across the West and Muslim world 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 with those in the West who put rights to freedom of expression above any religious offence caused.
"They hate him [the Prophet Muhammad] 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 its embassies, schools and cultural centres to shut in a score of countries.
'Cut him in pieces'
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 police officers, and more than 100 wounded, according to Allah Bachayo Memon, spokesperson 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 north-west city of Peshawar, clashing with riot police who fired tear gas. At least five people were killed.
In Mardan in the north-west, 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."
'Day of love'
Security forces fired in the air in Peshawar and the eastern city of Lahore to keep protesters away from US consulates. Police fired tear gas at about 1 000 protesters in Islamabad.
The US 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 Muhammad.
Pakistan 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 US chargé d'affaires to lodge a protest over the video posted on YouTube, the latest in an array of irritants poisoning US-Pakistani relations.
In neighbouring Afghanistan, police contacted religious and community leaders to try to prevent bloodshed. Protests in Kabul and the north 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 US and French flags and an effigy of US President Barack Obama.
Protests went off peacefully in the Arab world, where last week several embassies were attacked and the US envoy to Libya was killed in an initial burst of unrest over the film.
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 US embassy last week.
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 US embassy was stormed last week, several hundred Shi'ite protesters chanted anti-American slogans, but riot police blocked the route to the embassy.
'Death to America'
Anger over the film brought several thousand Shi'ites and Sunnis together in a rare show of sectarian unity in Iraq's south city of Basra, where they burnt US and Israeli 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".
The violence provoked by the film has led to a total of about 30 deaths so far, a United Nations official said.
"Both the film and the cartoons are malicious and deliberately provocative. The film particularly portrays a disgracefully distorted image of Muslims," Rupert Colville, spokesperson for UN 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. – Reuters