Since the arrival of the monitors, activists said security forces had continued to clash with anti-government protesters, with at least 15 people reportedly killed on Wednesday.
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The observers first visited the flashpoint town of Homs on Tuesday, where the team's leader Mustafa al-Dabi caused controversy by saying he had seen "nothing frightening" there, the BBC reported.
He later said he needed more time to assess the city, and during the team's second visit to Homs on Wednesday, they were met by “angry crowds, gunfire and explosions,” Al Jazeera reported.
Footage taken by activists was said to show monitors, dressed in orange vests, rushing behind a concrete building amid heavy shooting.
Other footage showed the body of five-year-old boy laid on the bonnet of a car used by the observers, Al Jazeera reported, adding the boy was said to have been killed in the presence of the mission in Homs.
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The ongoing violence led the credibility of the mission being questioned, and criticism that it is not doing enough to stop the government's crackdown on protests.
Reports say that protesters in Hama, which is north of Homs, have been prevented for two days from demonstrating by security forces firing tear gas and live ammunition.
One Homs activist told the BBC that speaking to the observers without the authorities knowing was difficult, and that the “inspectors are watched all the time” and that he would be caught and killed if found talking to them.
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The Arab League mission is the first international involvement on the ground in Syria since the protests began in March. There are 66 observers in Syria, a number that is expected to rise to between 200 and 300.
On Wednesday, Syrian state television reported that 755 detainees involved in "recent incidents" had been freed from custody.