At least 13 people have been killed in fresh violence across Syria, activists said, as Arab League observers continue their mission to visit flashpoint cities in the country.
Six of the dead were said to be taking part in an anti-government demonstration in the central city of Hama on Wednesday. Local rights groups say others were killed in Homs, Aleppo and Idlib.
Video shared by activists from the protest in Hama showed gunshots being fired and black smoke rising above the city. Dozens of men were marching through the streets, chanting "Where are the Arab monitors?"
In Deraa, the cradle of the nine-month uprising against President Bashar al-Assad's government, meanwhile, reports from a UK-based rights group indicate that army defectors killed at least four Syrian soldiers in an ambush.
The Arab League's observers were set to visit Homs, Hama and Idlib on Wednesday, Mustafa al-Dabi, the head of the mission, said.
World powers have been pressuring Damascus to give full access to the monitors if the government is intent on implementing a plan to end its crackdown on protests.
Video uploaded by Homs-based activists showed monitors visiting the restive Baba Amro neighbourhood, with heavy gunfire clearly audible in the background. Other videos showed residents of Baba Amro showing observers the body of a five-year-old boy who was reportedly killed by security forces.
Al-Dabi, who visited the central city of Homs with his team a day earlier, said the members of the mission "did not see anything frightning".
In-depth coverage of escalating violence across Syria
"Yesterday was quiet and there were no clashes. We did not see tanks but we did see some armoured vehicles," he said.
"But, remember, this was only the first day and it will need investigation. We have 20 people who will be there for a long time."
A Homs-based activist told the Reuters news agency that some families of people who have died in the violence there refused to meet with the monitors because they were being escorted by an army officer.
His statements came as activists reported the death of at least 42 people across the country on Tuesday, including 17 in Homs.
They charged that the army had pulled back heavy armour from the Baba Amro area of Homs ahead of the monitors' visit, accusing the regime of deception.
The French foreign ministry on Wednesday also made the same allegation, insisting that observers "must be allowed to return without delay to this martyr city, to travel everywhere in it freely and to have the necessary contact with the public".
Sergei Lavrov, the Russian foreign minister, also urged Syria to give the observers maximum freedom as they go about their mission in the violence-wracked country.
"We constantly work with the Syrian leadership calling on it to fully cooperate with observers from the Arab League and to create work conditions that are as comfortable and free as possible," Lavrov said.
The United States also demanded that Syrian authorities allow the mission full access and urged monitors to report what they find to the international community.
"Syrian authorities have transferred perhaps hundreds of detainees to off-limits military sites to hide them from Arab League monitors now in the country."
-Human Rights Watch
"We obviously look to these individuals to be intrepid in their search for the truth of what's happening on the ground," Mark Toner, the US State Department's deputy spokesman, said.
"The regime used the last several days as an opportunity to escalate their attacks on several ... neighborhoods in Homs and other cities prior to the deployment of these monitors," he added.
The Arab League plan endorsed by Syria on November 2 calls for the withdrawal of the military from towns and residential districts, a halt to violence against civilians and the release of detainees.
Syrian state television reported on Wednesday that the government has released 755 detainees "whose hands were not stained with blood".
But Human Rights Watch (HRW), a the US-based rights organisation, accused the government of hiding from the observers hundreds of detainees held in its crackdown on dissent.
"Syrian authorities have transferred perhaps hundreds of detainees to off-limits military sites to hide them from Arab League monitors now in the country," read an HRW statement.
Activists on Tuesday said Syrian police used tear gas to disperse an estimated 70,000 people who took to the streets of Homs as the observers visited.
Some demonstrators were fired at with live ammunition as they made their way to Sa’a square, and four were wounded, one seriously.
Before joining the march on Al-Sa'a square, tens of thousands staged a sit-in in al-Khalidiyeh neighbourhood, according to the Syrian Observatory for Human Rights (a London-based group), which also reported demonstrations in Bab Dreib and Jub al-Jandali districts.
At least 34 civilians were reportedly killed in Homs' Baba Amro district on Monday.
The UN estimates more than 5,000 people have been killed in the crackdown since anti-government protests began in mid-March.
The Syrian government says most of the violence has been perpetrated by "armed terrorist groups" that are working against the government.