Reports say at least 20 people have died as demonstrations against an anti-Islam video erupted across Pakistan, a day after protesters tried to storm the US embassy in the capital, Islamabad.
Tens of thousands of Pakistanis took to the streets across the country after the government called an impromptu public holiday to let people protest under the banner of "Love the Prophet Day".
In Karachi, armed protesters among a group of 15,000 fired on police, killing two officers, as at least 10 protesters died in the violence. The crowd also burned six cinemas, two banks, a KFC and five police vehicles.
Crowds armed with clubs and bamboo poles converged on the Firdaus picture house, "smashing it up and setting furniture ablaze", according to Gohar Ali, a police officer.
Witnesses said a separate rampaging crowd stormed the Shama cinema, notorious locally for showing films considered to be pornographic.
In the Pakistani city of Peshawar, police fired on rioters who were torching a cinema. Mohammad Amir, a driver for a Pakistani television station, was killed when police bullets hit his vehicle at the scene, said Kashif Mahmood, a reporter for ARY TV.
At least four protesters and one police officer were killed in the northwestern city, along with 40 injured and two cinemas and two shops torched.
In the capital Islamabad, some 19 protesters and eight police were injured. And in Lahore, at least five protesters were wounded.
Police on alert
"They do not want this anti-Islam video to be supported by the United States," said Al Jazeera's Kamal Hyder, reporting from Islamabad.
"Despite the fact that the American president has said that they have got nothing to do with it, the people here are very angry."
Al Jazeera's Rosiland Jordan reports on growing US concern
"The people want the government to be able to launch a protest, and they are saying they will not go home unless they get to the US embassy."
In Karachi, police told AFP news agency they had been on maximum alert and that bomb-disposal squads were sweeping planned locations of protests.
"All the entry and exit points of the city are heavily guarded. Helicopters are on stand-by for aerial surveillance," Fayyaz Laghari, provincial police chief, said.
"We have deployed our maximum police force to the sensitive parts of the city to ensure security during protest rallies today."
All the major political parties and religious groups had announced protests for Friday, as did many trade and transport organisations.
The previous day, the US embassy became the latest target of protesters angry at the YouTube video. The total number of protesters touched 5,000 with the arrival of protesters carrying the flags of anti-American Islamist groups.
At least 50 people were injured as police fired tear gas and live rounds towards the crowds.
US launches PR blitz
Al Jazeera's Rosiland Jordan, reporting from the US state department, said: "So there's a lot of concern that there could be real blowback against the US."
"The US has been very concerned about the prospect for demonstrations across Pakistan because of what has happened between the two countries in the past year."
Our correspondent continued: "Pakistan is one of those countries where anti-American sentiment is already quite high and certainly having this video - said to be the genesis for so many of these demonstrations across the region - doesn't help the US cause."
US Secretary of State Hillary Rodham Clinton met on Friday with Pakistan's foreign minister, who avoided an invitation to explicitly condemn the violence.
Speaking to reporters ahead of the meeting, Clinton called on "leaders and responsible people everywhere to stand up and speak out against violence".
Standing beside her, Pakistani Foreign Minister Hina Rabbani Khar focused her comments entirely on the film, which Muslims believe is blasphemous.
She thanked Clinton for speaking out against the video, saying it sent a "strong message" that should help end the violence.
"The last 18 months were very, very difficult," Khar said at the start of the talks Clinton, adding the nations were doing "better than we could have expected to do in rebuilding the trust".
Against this tense backdrop, the US bought time on Pakistani television stations to run a series of ads on Thursday in an effort to assuage Muslim feelings of hurt.
The US hopes the ad would show that the country had no involvement with the controversial internet video.
The US embassy in Islamabad spent about $70,000 to run the announcement, which features clips of US President Barack Obama and Secretary of State Hillary Clinton and underscores US respect for religion, declaring the US government had nothing to do with the video.
Obama is shown saying: "Since our founding, the United States has been a nation that respects all faiths. We reject all efforts to denigrate the religious beliefs of others."
Clinton then says: "Let me state very clearly, the United States has absolutely nothing to do with this video. We absolutely reject its contents. America's commitment to religious tolerance goes back to the very beginning of our nation."
Addressing a media briefing on the ad campaign, Victoria Nuland, state department spokeswoman, said the aim was "to make sure that the Pakistani people hear the president's messages and the secretary's messages".
'Feelings of dignity'
Meanwhile, the US closed its diplomatic missions across Indonesia due to continuing demonstrations over the anti-Islam film.
Protests also occurred on Friday by Sunni and Shia groups in Lebanon, where the Hezbollah movement organised a large rally in the city of Baalbek.
Elsewhere, some 10,000 Bangladeshis marched in Dhaka, 3,000 Iraqis took to the streets in the southern city of Basra, 2,000 Sri Lankans rallied in the capital Colombo and scattered demonstrations occurred in Afghanistan and Kashmir.
In Libya, rival demonstrations occurred by an anti-militia "Save Benghazi" group, and by the Salafi group Ansar Sharia, widely accused of being behind the attack on the US consulate in the eastern Libyan city.
Police cracked down on any planned rallies in the Tunisian capital, while some 200 Moroccans protested in Rabat's twin city of Sale.
In France, authorities had also outlawed any public demonstrations on Friday against the Prophet Muhammad cartoons.
But the German cities of Hannover, Munster and Freiburg had rallies by Muslims showing support for Muhammad.
Reporting from the city of Freiburg, Germany, Nick Spicer said, "Several hundred came to express their feelings of dignity and love for the Prophet".