At least 45 civilians were killed during renewed airstrikes on Aleppo early on Saturday, according to the Syrian Observatory for Human Rights, a British-based monitoring group.

The fierce aerial bombardment from Russian and Syrian warplanes has toppled several buildings in the besieged northern Syrian city.

The monitors warned that the death toll was likely to rise because a number of people remained trapped under rubble.

"There are planes in the sky now," Ammar al Selmo, the head of the Civil Defense rescue service in the opposition-held east, told the Reuters news agency on Saturday morning.

Harrowing scenes

A correspondent for the French news agency Agence France-Presse described one airstrike, at a market in the Bustan al-Qasr neighborhood, which left seven people dead and multiple body parts strewn at the site.

Medics said that they were carrying out many amputations to try to save the wounded and that supplies of blood and IV drips were running out.

Syrian forces and allied militia pushed on with their latest ground offensive following the failure of a US-Russian brokered ceasefire on Monday.

Analysts said Syrian President Bashar al-Assad's decision to launch an all-out assault on the last big urban area still in rebel hands marked a turning point in a conflict that was stalemated for years. Around 250,000 civilians are thought to remain trapped in eastern districts.

On Friday, at least 47 people were killed in heavy bombing, among them seven children, according to the Observatory, which described large-scale destruction in several rebel-held eastern areas.

This week's death toll has now reached at least 180, the observer group said.

Civilians remain trapped

Residents and activists described the use of a missile that produced earthquake-like tremors upon impact and razed buildings right down to basement level, where many residents desperately seek protection during bombing.

The UN children's agency UNICEF said the attacks had left nearly two million people without water.

Meanwhile, Syrian forces seized ground north of Aleppo on Saturday, capturing the Palestinian refugee camp of Handarat, which had been in rebel hands for years.

"Handarat has fallen," an official with one of the main Aleppo rebel groups told Reuters.

"The shelling and the raids did not stop. It is continuous," Bahaa al-Halabi, an activist in the east of the city, told the German news agency dpa.

Later on Saturday, rebels said they had recovered some or all of Handarat, while UK-based observers of the conflict said the battle was ongoing.

Condemnation from international community

A spokesman for United Nations chief Ban Ki-moon said he was "appalled by the chilling military escalation" in Aleppo.

In a statement, Ban warned that the use of bunker bust bombs and other advanced munitions against civilians may amount to war crimes. The UN head also considers this "a dark day for the global commitment to protect civilians."

But Syria's Foreign Minister Walid Muallem told the UN General Assembly on Saturday that he was confident of a military victory, because the army was making "great strides in its war against terrorism" on the ground, with help of "the true friends of the Syrian people" - Russia, Iran and Lebanon's Hezbollah. 

The Syrian government calls any individuals or groups fighting to overthrow the Assad regime "terrorists," including opposition groups backed by Western powers.

Speaking in Boston before a meeting with his counterparts from the European Union, the United Kingdom, France, Germany, and Italy, United States Secretary of State John Kerry said: "What is happening in Aleppo today is unacceptable. It's beyond the pale."

The top US diplomat had strong words for the Russian-backed Syrian regime. "If people are serious about wanting a peaceful outcome to this war then they should cease and desist bombing innocent women and children, cease cutting off water and laying siege in medieval terms to an entire community."

mm/jm, kl (AFP, AP, dpa, Reuters)