Syrian opposition forces said they were making a "tactical retreat" from a besieged district in Homs following a punishing, month-long military assault.
The anti-government fighters said on Thursday that they were running out of weapons and humanitarian conditions were catastrophic.
After days of appeals from humanitarian groups, the Syrian government has reportedly granted permission to the International Committee of the Red Cress to operate in Bab Amr on Friday.
Hisham Hassan, a Red Cross spokesman, told the Associated Press news agency on Thursday that the aid group recieved a "green light" to bring in emergency supplies and carry out evacuations of civilians affected by the governments attacks.
As the offensive on the central city of Homs intensified, Syria's main opposition group formed a military council to organize the armed resistance and funnel weapons to rebels, a sign of how deeply militarized the conflict has become over the past year as Syria veers closer to a civil war.
The Bab Amr rebels brigade said they were pulling out to spare some 4,000 civilians who insisted on staying in their homes. They said the decision was based on "worsening humanitarian conditions, lack of food and medicine and
water, electricity and communication cuts as well as shortages in weapons".
Homs is Syria's third-largest city with about 1 million people. Before the revolt began, activists estimated 100,000 people lived in Bab Amr. But many have fled over the past year and the population is believed to be much reduced.
The siege of Bab Amr has been among the deadliest of the uprising. Rebels had held the area for several months, but in early February, regime forces surrounded the neighborhood and began firing tank shells that slammed into
homes and killed hundreds of people.
Many of the wounded could not reach doctors, forcing residents to set up makeshift clinics for crowds of bloodied victims. The relentless attacks disrupted electricity, Internet and telephone services.
In-depth coverage of escalating violence across Syria
Burhan Ghalioun, head of the opposition Syrian National Council, told a news conference in Paris that rebels have relocated from some areas but said the resistance in Bab Amr "is still strong". It was not immediately clear
what escape route the rebels used.
Communication with residents in the district was difficult. Electricity and phone lines have been cut off, and an activist from the Syrian Network for Human Rights told Al Jazeera that the government was using a new technology to jam satellite phone signals.
Before the retreat was announced, Rami Abdul-Rahman, head of the British-based activist group Syrian Observatory for Human Rights, said there was "fierce fighting" at the entrances to Bab Amr.
In response to the worsening crackdown, the Syrian National Council, the largest opposition body, said it had formed a "military bureau" to organise the armed resistance against Assad.
The SNC said it wanted to funnel arms to rebel fighters in the country through the bureau.
"We know that some countries have expressed a desire to arm the revolutionaries.
The SNC, via its military bureau, wanted to organise this flow to avoid direct arms deliveries from particular countries," president Burhan Ghalioun said in Paris.
Al Jazeera's Nisreen el-Shamayleh, reporting from Jordan, said the SNC wanted to ensure it would supervise the arms supply and that the rebels were not armed haphazardly.
Samir al-Taqi, a former adviser to Assad, said he believed the president was probably getting most of his advice from the security apparatus and believed he could "decapitate the political opposition".
But he said the opposition seemed to be coming together.
"We have to understand that the uprising is a movement from bottom up and what is happening now in Syria is thousands and thousands of people are just pushed [into] the political arena. That's why they are for diversified or fragmented," Taqi told Al Jazeera.
'Disappointment' with Russia
The Syrian government's diplomatic isolation continued to grow with Switzerland and the United Kingdom both announcing the closure of their embassies.
William Hague, the United Kingdom's foreign minister, said British diplomats were being withdrawn from Syria for "security reasons".
Meanwhile, foreign ministers from Gulf countries planned to "express their disappointment" with Russia's stance on Syria during a meeting next week in Riyadh, the Saudi Arabian capital, with the Russian foreign minister, the Kuwaiti foreign minister said on Thursday.
Sabah Khaled al-Sabah spoke at an emergency session of the newly elected Kuwaiti parliament called to discuss the escalating crackdown.
Russia and China have twice wielded vetoes in the United Nations Security Council to block UN support for Arab League plans to usher a transition from Assad's rule.
Sabah said that Gulf nations would "call on Russia to take a position that will meet the aspirations of the Syrian people."
The United Nations Human Rights Council also condemned Syria for widespread violations that it said may amount to crimes against humanity and called for a halt to attacks against civilians.
The 47-member forum, holding an urgent debate, voted by 37 states in favour and three against, including China and Russia. The resolution was brought by Gulf countries. There were three abstentions, and four delegations did not take part in the vote. Syria was not present.