Syrian government forces and rebels fought battles in the centre of Aleppo and north of the city, a week into a Russian-backed offensive by the Syrian army to take the entire area.

There were conflicting accounts on the outcome of Friday's fighting.

The Syrian Observatory for Human Rights and a Syrian military source said government forces had captured territory north of Aleppo and buildings in the city centre.

An aerial bombardment of rebel-held areas continued on Friday, with heavy air strikes in the Shaar district where incendiary material struck a complex of medical buildings, the complex's director and other medical workers said.

Syrian state television reported that a child had been killed and others injured by rebel shelling in the government-held al-Ithaa neighbourhood of Aleppo.

Rebel sources however denied there had been any additional advances north of the city by government forces that seized the Handarat camp area north of Aleppo on Thursday. A rebel official said government forces had advanced in the Suleiman al-Halabi district of central Aleppo, but were then forced to withdraw.

Aleppo, Syria's largest city and commercial hub before civil war began in 2011, has been divided into government and opposition sectors for four years.

Russian Foreign Minister Sergei Lavrov told US Secretary of State John Kerry on Friday that Moscow is ready to consider additional ways to normalise the Aleppo situation.

Lavrov told Kerry over the phone that the ceasefire agreement brokered by Moscow and Washington had been violated numerous times in eastern parts of Aleppo by forces led by the group formerly known as the Nusra Front, the Russian foreign ministry added.

The Islamist Jabhat Fateh al-Sham group, formally known as the Nusra Front until it broke its formal allegiance to al-Qaeda in July, said that eight of its fighters had been killed fighting at Suleiman al-Halabi.

Lavrov told Kerry that Washington's failure to separate terrorists groups from the moderate opposition in Syria, had allowed Nusra to "hide behind other armed groups of the opposition with which Washington is cooperating," the ministry said.

Meanwhile, United Nations Secretary-General Ban Ki-moon said on Friday that he would establish an internal UN board of inquiry to investigate a deadly attack on a humanitarian aid convoy in Syria and urged all parties to fully cooperate.

"The Board of Inquiry will ascertain the facts of the incident and report to the Secretary-General upon the completion of its work. The Secretary-General will review the report and decide what further steps to take," UN spokesman Stephane Dujarric said in a statement.