Moscow and Damascus say halt in air strikes will continue to allow civilians and rebels to flee the besieged city.
Russia announced that it will broadcast live images of the evacuation of civilians and wounded people from besieged eastern Aleppo during a "humanitarian pause" it has scheduled for Thursday.
The planned pause would also be extended for an additional three hours to run from 0500 to 1600 GMT, General Sergey Rudskoi of the Russian General Staff said in a statement carried by the official Itar-Tass news agency on Wednesday.
The extension is intended to give United Nations and Red Crescent representatives enough time to evacuate sick and wounded people and civilians from the rebel-held enclave, Rudskoi said.
Activists and the Syrian Observatory for Human Rights, a UK-based monitoring group, have said few civilians made use of humanitarian corridors from eastern Aleppo previously announced by Russia.
The Syrian Foreign Ministry, meanwhile, said troops had pulled back from two designated humanitarian corridors to facilitate the transport of rebel fighters from eastern Aleppo to areas of their choice, Syrian state news agency SANA reported.
Rebels have said they will not leave eastern Aleppo, the last remaining major urban centre controlled by opposition forces.
The UN has said security fears, the fear of arrest, and the presence of Syrian troops at the corridors designated by Russia have prevented civilians from using them to leave the enclave.
Some 275,000 people are thought to be trapped in eastern Aleppo, with minimal access to food and medical care after hospitals have been repeatedly hit in air strikes, apparently by Russian or Syrian forces.
Youssef al-Youssef, of the rebel group Noureddine al-Zinki, described the new Russian announcement as "mere propaganda".
"This is not a truce. Eight hours to evacuate Aleppo is a request for surrender. This is totally rejected," said Zakaria Malhafji, a spokesman for the rebel group Fistaqim.
"We will not leave the city. We want a total truce and the entry of aid," he told the dpa news agency.
The Syrian regime and its Russian allies on Wednesday suspended air strikes on rebel areas in the divided city of Aleppo for the second successive day before Thursday’s planned humanitarian pause.
Aleppo has been the target of an intense campaign by the forces of Syrian President Bashar al-Assad and Russia since a US-Russian brokered ceasefire in the country fell apart on September 19.
Activists inside eastern Aleppo said government planes had dropped leaflets calling on fighters to leave "because they have no other choice".
Meanwhile, an unnamed diplomatic source told the Reuters news agency that Russian warships were headed to Syria in the largest military deployment since the end of the Cold War.
The fleet passed the Norwegian city of Bergen on Wednesday, the diplomat said, while Russian media has said it will move through the English Channel, past Gibraltar, and into the Mediterranean Sea to the Syrian coast.
"They are deploying all of the northern fleet and much of the Baltic fleet in the largest surface deployment since the end of the Cold War," the diplomat said on condition of anonymity.
"This is not a friendly port call. In two weeks, we will see a crescendo of air attacks on Aleppo as part of Russia’s strategy to declare victory there," the diplomat said.
Russia has said that the deployment will target Islamic State of Iraq and the Levant fighters in Syria.
But the NATO diplomat said the additional military firepower was designed to drive out or destroy the 8,000 rebels in Aleppo, the only large city still in opposition hands, and allow Russian President Vladimir Putin to start a withdrawal.
"With this assault, it should be enough to allow a Russian exit strategy if Moscow believes Assad is now stable enough to survive," the diplomat said.
The fleet off Norway includes Russia’s only aircraft carrier, the Admiral Kuznetsov, which is carrying jet fighters, and the Soviet-era nuclear-powered battle cruiser Pyotr Velikiy, or Peter the Great.
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