Russia's military has announced a three-hour daily halt in air strikes on Syria's Aleppo to allow humanitarian convoys in, but the United Nations said it was not nearly long enough to help trapped civilians.

"To guarantee total security for the convoys to Aleppo there will be humanitarian windows established from 1000 to 1300 local time starting tomorrow [Thursday] during which all military hostilities, aviation strikes and artillery strikes will be halted," Lieutenant General Sergei Rudskoy of the Russian army's general staff told journalists on Wednesday.

Rudskoy said that a road had been built to an area on the northern outskirts of Aleppo through the Castello shopping centre to "ensure safety and organise round-the-clock delivery of food, water, fuel, medicine and other necessities to the city's west and east".

The UN, which had earlier called for 48-hour weekly pauses for the aid deliveries, said the three-hour truce announced by Russia would not be enough to meet the needs of civilians.

"To meet that capacity of need, you need two lanes and you need to have about 48 hours to get sufficient trucks in," top UN aid official Stephen O'Brien told reporters on Wednesday.

O'Brien said he had not been fully briefed on the Russian proposal, but that there were complicated logistics to address, such as ensuring that lorry drivers have enough time to safely make the trip to the city and back.

READ MORE: Syrian rebels deny losing ground in Aleppo

"When we are offered three hours, you have to ask what can be achieved in that three hours," said O'Brien.

"Is it to meet the need or would it only just meet a very small part of the need?

Battles rage on

On Monday, President Bashar al-Assad sent thousands of reinforcements to mount a counterattack in Aleppo after rebels broke through government lines two days earlier.

Syrian rebel groups told Al Jazeera on Tuesday that they were fighting to hang on to key areas in the northern city as government forces and allies, including Moscow, escalated attacks.

A barrage of rocket fire from Syrian rebels killed at least 14 people and left dozens wounded on Wednesday in government-held neighbourhoods of the divided city, state media said.

Fighting struck the southern edges of Aleppo as opposition fighters and government forces geared up for a major protracted battle that could mark a turning point in the five-year war.

Syrian state news agency SANA said rebel fire on the regime-controlled district of Hamdaniyeh on Wednesday killed 13 people and wounded 25 others.

Rocket attacks on another government-held neighbourhood killed one person and wounded 12 others earlier in the day.



SANA said Russian and government planes targeted what they called "terrorist" positions in the city's south, as an AFP news agency journalist in Aleppo said intense air strikes and artillery fire could be heard.

But it was unclear if the major push for control of the city had begun.

Up to two million people in Aleppo have gone without running water for the past four days, UN agencies said, raising the risks of disease in a city already devastated by years of fighting.