BEIRUT (AP) -- Security forces opened fire Friday as thousands of anti-government protesters took to Syria's streets in a weekly ritual of defiance and demands for President Bashar Assad's ouster, activists said. They said at least 12 people, including two children, were killed in Damascus and elsewhere.

Four were killed in Barzeh, a Damascus district 3 miles (5 kilometers) from the city center, said Syria-based human rights activist Mustafa Osso. He said they were felled by security forces' guns. But Syrian state television said gunmen, otherwise unidentified, had opened fire on security personnel and civilians, killing three civilians and wounding several security force members.

Three other fatalities occurred in al-Kasweh, a suburb of the capital; four in the central city of Homs, and one in Hama, also in central Syria, said the the Local Coordination Committees, which track the Syrian protests. Protests in several other provinces also came under fire but it was not immediately clear whether there were casualties, said a spokesman for the group, Omar Idilbi.

The committees said the deaths included a 12-year-old boy, Rateb al-Orabi, killed when security forces fired on protesters in the Shammas neighborhood in Homs, and a 13-year old boy in al-Kasweh. The reports could not be independently verified.

"Our revolution is strong! Assad has lost legitimacy!" protesters chanted in the Damascus suburb of Zabadani, according to video posted on YouTube. Another showed protesters chanting: "Oh Bashar, you coward, pack your bags and go to Iran."

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The military crackdown has failed to silence a pro-democracy movement that has now lasted more than 100 days. The Syrian opposition says 1,400 people have been killed in the continuing government crackdown.

In northern Syria, activists said at least 15,000 people held a protest on the highway linking the country's two main cities, Damascus and Aleppo. Thousands marched in Amouda and Qamishli in the northeast and in other provinces, Osso said.

Dissidents reported a strong security presence in many locations. In Homs, all roads leading to the city center were reported blocked.

An eyewitness in Homs said protests took place in every city district Friday. He said hundreds of security personnel had been brought in by bus since early morning and encircled the city's center.

The witness said security forces fired smoke grenades in the Jouret al-Shiyeh district to disperse protesters. He said pro-government thugs converged on Homs neighborhoods from neighboring villages and were "provoking" protesters, who began blocking roads with rocks to keep them back. He spoke on condition of anonymity for fear of reprisals.

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In the central city of Hama, activists said a massive protest took place in the city's main Assi square. Online footage showed huge numbers of people gathered, many waving Syrian flags and crying for the regime's downfall. A large purple banner was unfurled over a building, reading: "Long live free Syria, down with Bashar Assad."

The video and other reports from inside Syria could not be independently verified, since the Damascus government has banned all but a few foreign journalists and restricted local media's reporting.

The Syrian regime blames foreign conspirators and thugs for the unrest, but the protesters deny any foreign influence in their movement, during which they say authorities also have detained 10,000 people.

The protests, which have occurred every Friday after weekly Muslim prayers, come as Syrian refugees stream across the border to safe havens in Turkey to escape a military sweep in Syria's northwest. More than 1,500 Syrian refugees crossed into neighboring Turkey on Thursday alone, boosting the number sheltered in Turkey to more than 11,700.

International condemnation on Damascus was mounting steadily. The European Union announced Thursday it was slapping new sanctions on the Syrian regime and U.S. Secretary of State Hillary Rodham Clinton said the movement of Syrian troops right up to the Turkish border could prove dangerous, as concerns of possible confrontations grew.

(See: EU preparing new sanctions on Syrian companies)

Citing residents on the ground, Osso said the military has deployed heavily in areas across the border from Turkey and set up checkpoints. He said the few thousand people who had been on the Syrian side of the border had all fled into Turkey.

"The few who did not were arrested," he said, adding 100 people were arrested in the past two days.

Anticipating an exodus from Syria's second city, Aleppo, Turkish officials were setting up a sixth camp with up to 800 tents near a border crossing.

On Thursday, Syrian soldiers patrolled in military vehicles and on foot around the border village of Khirbet al-Jouz, according to Associated Press journalists who watched their movements from the Turkish side. The Local Coordinating Committees said residents reported tanks had entered the village and snipers were spotted on rooftops Thursday.

The Syrian army's operation was the closest Syrian troops had come to Turkey since the military crackdown in the area began two weeks ago as President Assad's forces tried to snuff out the opposition's chances of gaining a territorial foothold for a wider rebellion. The army's main thrust came against the town of Jisr al-Shughour, where armed anti-government resistance flared in early June.

Turkish Foreign Minister Davutoglu told reporters Friday he had conveyed Turkey's "concerns and thoughts" about the operation near Turkey's border in a telephone conversation with his Syrian counterpart on Thursday.

He said he would continue to talk to Syrian officials to ensure that "reforms and peace are brought about as soon as possible."

"We hope that Syria is successful in renewing itself in a stable manner and comes out of the situation stronger. We will do all that we can to help," he said.

In Brussels, the EU said it had expanded its anti-Syrian sanctions list, targeting seven more individuals and four companies, bringing to 34 the number of people and entities faced with an asset freeze and travel ban, including Assad.

The EU also has an embargo on sales of arms and equipment that can be used to suppress demonstrations.

In the government's latest bid to blunt the demonstrations, Foreign Minister Walid Moallem on Wednesday reiterated Assad's call for national dialogue and spoke of democracy within months - a bold assertion after more than four decades of authoritarian rule by the Assad family and months of bloody reprisals.

A skeptical opposition rejected the overture while the Syrian military is occupying towns and shooting protesters.

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Associated Press writer Mehmet Guzel contributed to this report from Guvecci, Turkey.

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