BEIRUT — After a punishing, monthlong military siege, Syrian rebels made what they called a “tactical retreat” Thursday from a key district in Homs, saying they were running low on weapons and the humanitarian conditions were unbearable.

Within hours of the rebels’ withdrawal, President Bashar Assad’s regime granted permission for the International Committee of the Red Cross to enter the neighborhood of Baba Amr, which had become a symbol of the resistance.

Human rights workers have been appealing for access for weeks to deliver food, water and medicine, and to help evacuate the wounded from an area that has been sealed off and attacked by the government since early February.

The Red Cross and the Syrian Arab Red Crescent received a “green light” from the Syrian authorities to enter Baba Amr on Friday “to bring in much-needed assistance including food and medical aid, and to carry out evacuation operations,” ICRC spokesman Hicham Hassan said in Geneva. Also Thursday, Syria’s main op position group, the Syrian National Council, formed a military bureau to help organize the armed resistance and funnel weapons to rebels — a sign of how deeply militarized the conflict has become over the past year.