Warplanes bombed a strategic camp on the northern edge of Aleppo on Sunday as Syrian government forces, backed by Russia, battled rebels for control of the city as the U.N. Security Council met to discuss the escalating violence.
Russia's support of the latest offensive by Syrian forces since an international ceasefire collapsed last week appears to have buried any hope for diplomacy. The rebels said any peace process would be futile unless the "scorched earth bombing" stopped immediately.
Capturing the rebel-held half of Syria's largest city, where more than 250,000 civilians are trapped, would be the biggest victory of the civil war for President Bashar Assad's forces.
They have achieved their strongest position in years thanks to Russian and Iranian support and launched a fresh offensive for a decisive battlefield victory on Thursday. In the first major advance, they seized control of the Handarat Palestinian refugee camp, north of Aleppo.
Rebels counter attacked and said on Sunday they had retaken the camp before the bombing started.
"We retook the camp, but the regime burnt it with phosphorous bombs," said Abu al-Hassanien, a commander in a rebel operations room that includes the main brigades fighting to repel the army assault.
The army, which is being helped by Iranian-backed militias, Lebanon's Shiite Hezbollah militant group and a Palestinian militia, acknowledged rebels had retaken Handarat.
"The Syrian army is targeting the armed groups' positions in Handarat camp," a military source was quoted on state media as saying.
Planes also continued to pound residential areas on Sunday, flattening buildings, rebels and residents said. They say airstrikes have intensified, with more powerful weapons, since the new offensive began.
"The Assad regime and with direct participation of its ally Russia and Iranian militias has escalated its criminal and vicious attack on our people in Aleppo employing a scorched earth policy to destroy the city and uproot its people," a statement signed by 30 mainstream rebel groups said on Sunday.
The Syrian Observatory for Human Rights, a monitoring group, said at least 45 people, among them 10 children, were killed in eastern Aleppo on Saturday.
The army says it is targeting only militants.
Hundreds of thousands of people have been killed in the civil war and 11 million driven from their homes.