Lima (AFP) - US National Security Advisor Susan Rice condemned "heinous" bombings of hospitals in rebel-held eastern Aleppo Saturday, warning the regime and its Russian backers they are responsible for immediate and long-term consequences.

"The United States condemns in the strongest terms these horrific attacks against medical infrastructure and humanitarian aid workers. There is no excuse for these heinous actions," Rice 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."

Her comments come as intense government air strikes and artillery fire killed at least 27 people in Aleppo, where hospitals have been destroyed and schools have been forced to close.

An AFP correspondent on the ground described relentless bombardment with air strikes, mortar rounds and barrel bombs slamming into residential neighborhoods in the east of the battered second city.

Rice indicated that the US government would use a summit of Asia-Pacific leaders in Peru to put pressure on Russia. President Vladimir Putin is attending the event.

"The United States again joins our partners, many of them gathering in Peru this weekend, in demanding the immediate cessation of these bombardments and calling on Russia to immediately deescalate violence and facilitate humanitarian aid and access for the Syrian people," said Rice.