Syria’s government pounded rebel-held Aleppo with air strikes
and artillery fire on Saturday, killing 27 people and prompting Washington to
condemn the “heinous actions” of Damascus and its ally Russia.

UN officials said they were “appalled” by the
escalating violence and urged access to east Aleppo, where more than 250,000
people have been under siege for nearly four months.

Since it began on Tuesday, the assault on the rebel-held
east of Aleppo has damaged hospitals, forced schools to close, and killed
nearly 100 civilians, according to a monitor.

A correspondent described relentless bombardment with air
strikes, mortar rounds and barrel bombs slamming into residential
neighbourhoods where residents cowered at home.

“It is a catastrophic day in besieged Aleppo with
unprecedented bombardment with every type of weapon,” a member of the
White Helmets rescue group said in a video posted on the organisation’s
Facebook page.

US National Security Advisor Susan Rice said Washington
condemned “in the strongest terms these horrific attacks against medical
infrastructure and humanitarian aid workers.”

“There is no excuse for these heinous actions,”
she said in a statement.

“The Syrian regime and its allies, Russia in
particular, bears responsibility for the immediate and long-term consequences these
actions have caused in Syria and beyond.”

Moscow says it is not involved in the current assault on
Aleppo, concentrating its firepower on opposition and jihadist forces in
neighbouring Idlib instead.

But Damascus and its allies have made clear they want rebels
expelled from eastern Aleppo, which fell from regime control in mid-2012.

Once Syria’s economic powerhouse, Aleppo has been ravaged by
the war that has killed more than 300,000 people since it began with
anti-government protests in March, 2011.

No aid has entered east Aleppo since government forces
surrounded it in July, and residents report shortages of food and fuel, as well
as lengthy power outages and water shortages.

Two top UN officials said they were “extremely saddened
and appalled by the recent escalation in fighting in several parts of
Syria”.

Humanitarian coordinator for Syria Ali al-Za’atari and
regional humanitarian coordinator Kevin Kennedy also said they had shared a
plan to deliver aid, and evacuate the sick and wounded from east Aleppo.

“It is imperative that all parties agree to the plan
and allow us to secure immediate, safe and unimpeded access to provide relief
to those most in need,” they said.