The Red Cross said Tuesday it was "appalled" by escalating violence in Syria's Aleppo and was awaiting government permission to deliver aid to the pre-war commercial hub.
In a statement, the Geneva-based organisation did not assign any blame for mounting casualties in Aleppo, but it urged all parties to observe international law.
The International Committee of the Red Cross said it was "appalled by a sharp escalation of violence in the northern city of Aleppo where parties have in recent days carried out indiscriminate attacks against civilians."
Boris Michel, ICRC's delegation head in Syria, said the violence was "unacceptable" and had led to hundreds of civilian casualties.
He urged parties to the fighting in the city to protect civilians and essential infrastructure, including power plants and medical facilities.
In recent weeks, the Syrian government has stepped up a campaign of aerial bombardment of rebel-held parts of eastern Aleppo city.
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The campaign began in December and has killed hundreds of people and forced thousands to flee their homes.
Over the same period, rebel fighters have targeted government-held districts in the west of the city with rocket fire and attempted to advance in some parts of western Aleppo.
The Red Cross said the fighting had led to the closure of the only crossing between the two sides of the city, further limiting civilian access to food, medicine and water.
"The ICRC and the Syrian Arab Red Crescent stand ready to deliver relief aid to Aleppo residents, and to local medical facilities, but are unable to do so owing to the lack of necessary support by the parties," the statement said.
"Despite our uninterrupted efforts over the last two months to gain access to areas directly affected by the fighting in Aleppo and rural Aleppo, we are still waiting for a green light from the government to deliver urgently needed relief," Michel added.
The United Nations estimates more than nine million Syrians are in need of humanitarian assistance, are trapped under siege or in areas caught in brutal fighting.
More than 150,000 people have been killed since Syria's conflict began in March 2011, according to the Syrian Observatory for Human Rights.