The move comes amid intensified air strikes
The Syrian government has approved a United Nations aid plan, but with restrictions.
Damascus has given a green light for UN convoys to deliver aid to 25 of 29 besieged and hard-to-reach areas across Syria, diplomats said.
But, crucially, not to the eastern districts in Aleppo that are controlled by rebels.
The move by Damascus comes amid intensified Syrian and Russian air strikes targeting rebel-held districts of the city.
In the last two days of bombing, at least 145 people were killed, according to the head of the Civil Defence rescue service there, Ammaral Selmo.
"The bombing has been very intense," he said.
And four children died when shells landed near a school in government-held western Aleppo, the Syrian Observatory for Human Rights has said.
Aleppo, a northern city that was once a thriving trade hub, has become a central battleground in the five-year-Syrian war and is facing a humanitarian disaster.
The city's mayor has spoken of a "holocaust", and the UN has warned it could be destroyed by Christmas is the onslaught continues.
The besieged population of 275,000 - including 100,000 children - is in desperate need of food, water and medical supplies.
A US-Russia brokered ceasefire crumbled almost immediately, and the Syrian government launched an assault to capture rebel-held areas in the east of the city.
US Secretary of State John Kerry broke off talks with Russian Foreign Minister Sergei Lavrov over the offensive, which has included air strikes on hospitals.
The US and France say the offensive amounted to war crimes for which Syria and Russia were responsible.
Nevertheless, Mr Kerry will meet his Russian counterpart in Switzerland on Saturday to discuss the crisis.
And French Foreign Minister Jean-Marc Ayrault held talks with Mr Lavrov and stressed the need "to achieve a halt to the bombing of Aleppo to allow access for humanitarian aid" and resume negotiations.