Northern Syria (CNN) -- Forces loyal to President Bashar al-Assad's regime shelled Syria's largest city Thursday, as rebels said they had pulled back for tactical reasons from portions of a hotspot neighborhood there.
Two members of the Free Syrian Army said that its fighters had withdrawn from the front line in the flashpoint area of Salaheddine, but that reinforcements were en route from elsewhere in Aleppo to launch a counterstrike.
The Syrian government and rebel groups have been battling for days to control Aleppo, a key front in a conflict that has morphed into a civil war since government forces began cracking down on peaceful protesters in March 2011.
Shelling was reported Thursday in Salaheddine and other areas, said the Syrian Observatory for Human Rights, a London-based opposition group.
Abu Ayham al-Halaby, a Free Syrian Army commander in Aleppo, told CNN the FSA had retreated from a portion of Salaheddine for tactical purposes and to avoid the heavy shelling.
An FSA fighter known as Louay said rebel forces had pulled back several blocks in the neighborhood but were preparing for a counterattack. He reported a pause in the shelling that had been pounding the area.
Abu Omar, a spokesman for the Syrian National Council in Aleppo, said the fighters had withdrawn from "most of Salaheddine district, mostly because they are running out of ammunition, but also for tactical reasons." He said the shelling was halted because regime forces were advancing into Salaheddine on foot.
Along with Salaheddine, the Sukari and Bustan al-Qaser areas have been heavily shelled by Syrian army artillery, helicopters and fighter jets, al-Halaby said. Opposition activists and fighters reported shelling in the Al-Sha'ar, Bab al-Hadid, and Anjara areas and in central neighborhoods near the historic Aleppo castle.
The FSA has destroyed at least three tanks in those central neighborhoods, al-Halaby said.
Shelling in the Salhiyeen neighborhood killed several people, most of them women and children, said the Local Coordination Committees of Syria, a Syrian-based opposition activist network.
At least 134 people were killed Thursday across Syria, including 47 in Aleppo, the LCC said. It had earlier reported 142 dead.
Roughly 17,000 people have been killed since the fighting began, the United Nations said last month. The opposition has put the toll at more than 20,000. At least 141 people were killed Wednesday, including 30 in Aleppo, the LCC said.
The violence has sparked mass displacement, with people fleeing to safer places in Syria and escaping to Turkey, Lebanon, Jordan and Iraq. The Turkish government says more than 50,000 Syrians are living in Turkish refugee camps.
The warfare has taken a toll on al-Assad's regime, which has been hit by assassinations and political and military defections.
The latest high-level defection came from Riyad Hijab, who had assumed the position of prime minister two months ago. Citing the "killing and terrorist regime," he defected Wednesday to Jordan.
On Thursday, Syrian state television reported that al-Assad has appointed Health Minister Wael al-Halaki to replace Hijab as prime minister.
Countries in the West and the Middle East have been critical of the al-Assad regime but have not intervened militarily. The Obama administration has come under fire from some members of Congress for taking what they say is a "hands-off approach" toward Syria.
Susan Rice, the U.S. ambassador to the United Nations, said Thursday that the United States doesn't want the U.N. unarmed observer mission in Syria to be extended past its August 19 mandate, but that it is open to some other kind of U.N. presence.
"The conditions, particularly the extreme use of violence and heavy weapons by the government, do not permit the UNSMIS (U.N. Supervision Mission in Syria) monitors — or any monitors at this point who are unarmed — to do the job they were sent to do," she told reporters.
The Security Council had approved in April the deployment of 300 unarmed observers to monitor a ceasefire that was called for in a peace plan negotiated by Kofi Annan, who was then acting as the U.N.-Arab League envoy. But the ceasefire fell apart, the fighting continued and the UN scaled back its observer force to 150.
Its numbers will be reduced to 100 by August 14, the U.N.'s Department of Peacekeeping said Thursday.
The United States has provided only nonlethal aid such as communications equipment. But recent actions and rhetoric hint at more action.
President Barack Obama signed a covert directive authorizing U.S. support for Syrian rebels, U.S. officials told CNN last week. The secret order, referred to as an intelligence "finding," allows for clandestine support by the CIA and other agencies.
John Brennan, Obama's chief counterterrorism adviser, said Wednesday that all options, including the possibility of imposing a no-fly zone, remained under consideration.
Iran, a supporter of the al-Assad regime, hosted a conference on the conflict Thursday in Tehran.
Among the representatives of more than two dozen countries attending were the foreign ministers of Pakistan, Zimbabwe and Iraq, state-run Islamic Republic News Agency said. China and Russia, also allies of Damascus, were among the nations to send delegates to the conference.
But nations critical of the regime, such as the United States, France, Britain, Turkey, Saudi Arabia, and Qatar, were absent.
A statement from the conference emphasized "the necessity of pursuing political solutions based on national dialogue as the only way to resolve the Syrian crisis with the main objective of bringing the violence to a total end and encouraging the two sides to prepare the ground for the national dialogue."
The statement championed "non-intervention in domestic affairs of other countries and the respect of their national sovereignty and territorial integrity."
It also expressed "serious concern over the entry of known terrorist groups and sects into the Syrian conflict and seriously warning of the spread of terrorism and its dire consequences on the peace and security of the region." Syria has consistently blamed violence in the country on "terrorist groups."
Iranian officials, meanwhile, visited capitals in the region to discuss Syria and get help to free dozens of Iranians abducted over the weekend by rebels in Syria.
Iranian media initially reported that the 48 captives were pilgrims on a visit. In a televised video later, Syrian rebels claimed responsibility for the kidnapping, saying the captives were not pilgrims, but were members of Iran's Revolutionary Guard. Salehi said they included retired members of the Guard, the semi-official Iranian Students' News Agency reported Wednesday.
Three of the 48 Iranians were killed during shelling in the Damascus suburbs, the LCC said.
CNN's Amir Ahmed, Kareem Khadder, Ben Wedeman, Salma Abdelaziz, Ivan Watson, Hamdi Alkhshali, Yesim Comert and Joe Sterling contributed to this report.