The German government said on Wednesday that Moscow had the power to stop the final sweeping advance on the northern Syrian city in recent days but had failed to do so.

"We know that this ruthless destruction of eastern Aleppo would not have been possible without massive military support from Russia," German Chancellor Angela Merkel's spokesman Steffen Seibert said.

"Russia has not prevented the crimes of the last few days although it was within its power to do so," he told a news conference in Berlin.

Seibert's comments came hours after monitors and activists in eastern Aleppo described fresh airstrikes and heaving shelling on Wednesday, despite a Russian-Turkish brokered ceasefire, which was declared on Tuesday to allow residents of the city to evacuate.

Seibert said the option of imposing sanctions on Moscow over its role in the Syria conflict was still on the table, but he added that the immediate priority was to help civilians trying to flee the city.

No more talks with United States

Fresh from negotiating the latest truce, Russian Foreign Minister Sergei Lavrov said the prospect of fresh talks with the United States over Syria would be "pointless."

He hoped progress with Turkey could be "more effective than many months of a pointless hangout we have had [with] the United States," Russian news agencies cited Lavrov as saying.

Later on Wednesday, Turkey said President Recep Tayyip Erdogan and Russian President Vladimir Putin had agreed in a phone call that violations of the ceasefire deal must stop.

The pair was to make a joint effort to start the evacuation of civilians and opposition forces as soon as possible, Turkish presidential sources said.

But Syrian President Bashar al-Assad claimed that the latest lull in the fighting was part of a Western plan aimed at stopping his government's advance in the city, telling Russian TV that the truce would "keep the terrorists and save them."

Despite the apparent military success for Assad and his allies in eastern Aleppo, German Foreign Minister Frank-Walter Steinmeier on Wednesday said that the country's longtime leader should not be part of the process to resolve the nearly 6-year conflict.

"I can not imagine, that the political future of Syria with (Assad) can be be created," Steinmeier said.

'Onus on Syrian regime' to protect civilians

Also on Wednesday, United Nations war crimes investigators said it was up to the Syrian government to prevent further attacks and reprisals in eastern Aleppo, following what it said were "numerous reports of violations," including summary executions, arbitrary arrests and enforced disappearances. Some may constitute war crimes, the world body said.

UN investigators had also received allegations that rebel groups had prevented civilians from leaving the area and of fighters embedding themselves within the civilian population, increasing the risk to civilians.

Meanwhile, French President Francois Hollande joined an international call for independent observers to oversee the evacuation of eastern Aleppo's residents.

He backed up similar comments by European Union foreign policy chief Federica Mogherini, who said, "The priority now, in these hours, is to protect civilians, guarantee them safe and monitored transit to a place of safety."

French government spokesman Stephane Le Foll said France and Germany were pressing for the creation of humanitarian corridors allowing civilians out and aid agencies into the battered city.

mm/sms (AFP, AP, Reuters)