Syrian forces loyal to President Bashar Assad fired on a group of Arab League monitors in a Damascus suburb, according to a report.
Al-Arabiya TV said Friday the observers, who are in the country to assess whether the regime is abiding by a promise to end 10 months of violence against pro-democracy protesters, were touring the streets in the Arbeen district of the capital.
They reportedly withdrew after the attack. There was no immediate word on casualties.
Meanwhile, Qatar's prime minister said the monitors' mission in Syria had made "some mistakes" and that he was turning to the United Nations for help.
Video: Thousands protest Assad regime in Syria (on this page)
Qatari Prime Minister Sheik Hamad bin Jassem Al Thani discussed the month-long mission with U.N. Secretary General Ban Ki-moon in New York on Wednesday amid mounting criticism that the observers are simply giving the Syrian regime cover for its ongoing crackdown on the uprising.
"We are coming here for technical help and to see the experience the U.N. has, because this is the first time the Arab League is involved in sending monitors, and there are some mistakes," he said, according to Kuwait's state news agency.
Asked what kind of mistakes, he replied: "This is the first experience for us. I said we have to evaluate what sorts of mistakes we have (made). There is no doubt for me. I can see there are mistakes, but we went there not to stop the killing, but to monitor."
Qatar has been at the forefront of criticism of Syria and has pushed for Arab League sanctions against Damascus.
Despite the criticism from Qatar's prime minister, the team of peace monitors will stay in Syria to check on the government's compliance with the Arab League peace accord — an agreement to scale back Syrian military presence in cities and free thousands of prisoners detained since the uprising began last March.
The league's special committee on Syria is due to meet in Egypt on Sunday to debate the initial findings of the mission, which has been criticized by Syrian activists who question its ability to assess the violence on the ground.
The activists said the teams did not have enough access and were escorted by Syrian authorities, who were manipulating them and hiding prisoners in military facilities.
Syria's opposition has also accused the regime of misleading the monitors by taking them to areas loyal to the government, changing street signs to confuse them, painting army vehicles blue to look like those of police and sending supporters into rebellious neighborhoods to give false testimony.
An Arab League official said the observers have not reported or complained about being misled by the regime. He said the Syrian opposition is making pre-emptive statements, fearing the regime might try to mislead the monitors.
Addressing the opposition's complaint about painting military vehicles blue to appear as police vehicles — something that has been seen on amateur videos — the official said: "Observers know what is for the army and what is for police." The official spoke on condition of anonymity because he was not authorized to speak to the media.
He added that additional monitors will head to Syria on Friday to raise the total numbers of observers to about 140.
U.N. spokesman Martin Nesirky told reporters in New York that Qatar's Sheik Hamad and Ban discussed "practical measures how the United Nations could assist this observer mission."
"The form that could take is that, under the auspices of the Office of the High Commissioner for Human Rights, there would be training of (Arab League) observers," he said. "This would be a small-scale undertaking to train observers."
An Arab government representative told Reuters on condition of anonymity that the monitors could not be withdrawn whatever the contents of the initial report.
Syria, keen to show it is respecting the accord, said it had released a further 552 people detained during the revolt against Assad "whose hands were not stained with blood".
Syria also said it provided the monitors with all the facilities they needed.
"What we are looking for is objectivity and professionalism," Foreign Ministry spokesman Jihad Makdesi told Lebanese Manar television.
State news agency SANA said some 4,000 detainees had been released since November.
Arab League General Secretary Nabil Elaraby said on Monday the mission had secured the release of about 3,500 prisoners. Campaign group Avaaz said on Thursday 37,000 people detained since March were still being held.
Reuters and The Associated Press contributed to this report.