At least 15 people have been killed in Pakistan in clashes during protests over an anti-Muslim film.
Police fired tear gas and live ammunition at thousands of demonstrators who threw rocks and set fire to buildings. Dozens were injured.
Muslims also marched in at least a half-dozen other countries, with some burning American flags and effigies of US President Barack Obama.
Pakistan has experienced nearly a week of deadly protests over the film, Innocence of Muslims, that has sparked anti-American violence around the Islamic world since it emerged on the internet in the past 10 days.
The deaths of at least 45 people, including the US ambassador to Libya, have been linked to the violence over the film, which was made in California and denigrates the Prophet Mohammed.
The Pakistani government declared today to be a national holiday - "Love for the Prophet Day" - and encouraged peaceful protests.
The US Embassy spent 70,000 dollars (£43,000) for advertisements on Pakistani TV that featured Obama and Secretary of State Hillary Clinton denouncing the video.
The deadliest violence occurred in the southern port city of Karachi, where 12 people were killed and 82 wounded, according hospital officials.
Armed demonstrators among a crowd of 15,000 in that city fired on police, according to police. The crowd also burned two cinemas and a bank.
Three people were killed and 61 wounded in the north-western city of Peshawar, where police fired on rioters who set fire to two cinemas and the city's chamber of commerce, and damaged shops and vehicles.
One of the dead was identified as Mohammad Amir, a driver for a Pakistani TV station who was killed when police bullets hit his vehicle, which was parked near the cinema.
Police beat demonstrators with batons. Later in the day, tens of thousands of protesters converged in a neighbourhood and called for the maker of the film, an American citizen originally from Egypt, to be executed.
Police and stone-throwers also clashed in Lahore and Islamabad, the capital. Police fired tear gas and warning shots to try to keep them from advancing toward US missions in the cities.
Police clashed with over 10,000 demonstrators in several neighbourhoods, including in front of a five-star hotel near the diplomatic enclave where the US Embassy and other foreign missions are located. A military helicopter buzzed overhead as the sound of tear gas being fired echoed across the city.
The government temporarily blocked mobile phone service in 15 major cities to prevent militants from using phones to detonate bombs during the protests.
Pakistan's Foreign Ministry today summoned the US charge affaires in Islamabad, Richard Hoagland, over the film. Pakistan has banned access to YouTube because the website refused to remove the video.
Pakistani Prime Minister Raja Pervaiz Ashraf had urged the international community to pass laws to prevent people from insulting the prophet.
"If denying the Holocaust is a crime, then is it not fair and legitimate for a Muslim to demand that denigrating and demeaning Islam's holiest personality is no less than a crime?" Mr Ashraf said in a speech to religious scholars and international diplomats in Islamabad.
Denying the Holocaust is a crime in Germany, but not in the US
US officials have tried to explain to the Muslim world how they strongly disagree with the anti-Islam film but have no ability to block it because of free speech guarantees.
In Iraq, about 3,000 protesters condemned the film and caricatures of the prophet that were published in a French satirical weekly. The protest in the southern city of Basra was organised by Iranian-backed Shiite groups. Some protesters raised Iraqi flags and posters of Iran's supreme leader, Ayatollah Ali Khamenei, while chanting: "Death to America."
Protesters burned Israeli and US flags and raised a banner that read: "We condemn the offences made against the prophet."
In the Sri Lanka capital of Colombo, about 2,000 Muslims burned effigies of Obama and US flags at a protest after Friday prayers, demanding that the United States ban the film. In Bangladesh, more than 2,000 people marched in the capital, Dhaka, and burned a makeshift coffin draped in an American flag and an effigy of Obama.
They also burned a French flag to protest at the publication of the caricatures of the prophet. Small and mostly orderly protests were also held in Malaysia and Indonesia.
Thousands gathered in Lebanon's Bekaa Valley for the latest in a series of rallies organised by the Shiite militant group Hezbollah. Protesters carried the yellow Hezbollah flag.
Hezbollah appeared to be trying to ensure the gatherings don't become violent, planning them only in areas where Hezbollah has control. None of the rallies targets the heavily fortified US Embassy in the hills outside Beirut.
Police clamped a day-long curfew in parts of Indian-controlled Kashmir's main city, Srinagar, and chased away protesters. Authorities in the region also temporarily blocked mobile phone and internet services to prevent viewing the film clips.
Iranian President Mahmoud Ahmadinejad also lashed out at the West over the film and the caricatures in the French weekly, Charlie Hebdo.
"In return for (allowing) the ugliest insults to the divine messenger, they - the West - raise the slogan of respect for freedom of speech," said Ahmadinejad during a speech in the capital, Tehran.
He said this explanation was "clearly a deception."
In Germany, the Interior Ministry said it was postponing a poster campaign aimed at countering radical Islam among young people due to tensions caused by the online video insulting Islam. It said posters for the campaign - in German, Turkish and Arabic - were meant to go on display in German cities with large immigrant populations today but are being withheld because of the changed security situation. Germany is home to an estimated four million Muslims.