BEIRUT — Syrian state media are saying that rebel shelling of government-held neighborhoods of the northern city of Aleppo has killed six people and wounded 47.

State TV says some of the shells hit the dorms area at the Aleppo University on Tuesday, killing two students and wounding eight. The Britain-based Syrian Observatory for Human Rights, an activist group that tracks the civil war, says two people were killed in the shelling.

Aleppo has been the focus of the fighting in recent months as governed forces have besieged all eastern, rebel-held neighborhoods of the city. Syria's largest.

The Observatory says 420 people have been killed and more than a thousand have been wounded in and around Aleppo since a cease-fire brokered by Russia and the U.S. collapsed two weeks ago. Most of the dead have been in rebel-held parts of the city, which has been pounded by Syrian and Russian warplanes.

The U.N. human rights chief is decrying an unfolding "calamity" in the embattled Syrian city of Aleppo where government forces continue to strike besieged, rebel-held parts in the east.

Zeid Ra'ad al-Hussein in an appeal on Tuesday called for initiatives such as preventing U.N. Security Council's permanent members from vetoing council resolutions to help prevent severe crimes.

He says the Security Council should adopt rules to limit veto use in cases of war crimes, crimes against humanity or genocide. Russia, an ally of Syria's government, holds veto power along with the United States, France, Britain and China.

Zeid says that attacks over the last 10 days in rebel parts of Aleppo, including airstrikes by Syrian and Russian forces, have been "the most intense" there since Syria's civil war began in 2011.

Syrian rebels say pro-government forces are pressing their assault on the eastern, rebel-held neighborhoods of Aleppo, this time attacking the city from the south in a bid to penetrate opposition-controlled areas.

The Islamic Front rebel coalition said on Twitter on Tuesday that its factions repelled an advance on the Sheikh Saeed neighborhood.

The Britain-based Syrian Observatory for Human Rights says the government offensive is accompanied by airstrikes on the contested neighborhoods.

The monitoring group says more than 400 civilians have been killed in and around Aleppo since the collapse of a U.S. and Russian-brokered cease-fire two weeks ago, mainly in the rebel-held east of the embattled city.

In the offensive, health facilities and hospitals have repeatedly come under attack.