DAMASCUS — Syria’s military backed by Russian warplanes have killed more than 150 people in eastern Aleppo this week say rescue workers, part of a renewed bombardment supporting an offensive to seize the city’s shattered rebel-held sector.

As air strikes and shelling of the city’s east intensified since Tuesday after a brief period of relative calm, Syria’s government approved a U.N. plan to allow aid convoys into most besieged areas of Syria, with the exception of Aleppo.

Rising casualties in Aleppo, where buildings have been reduced to rubble or are lacking roofs or walls, have caused international outcry and a renewed diplomatic push, with talks between the United States and Russia planned in Switzerland for Saturday.

Now in its sixth year, Syria’s civil war has killed 300,000 people and made millions homeless while dragging in regional and global powers and inspiring jihadist attacks abroad.

European Union foreign ministers drafted a statement accusing Syria and its allies of violence that “may amount to war crimes”.

But Russian Vladimir Putin president dismissed the allegations, blaming the United States for the crisis. 

“It’s political rhetoric that does not mean much and does not take into account the realities in Syria,” told France’s TF1 TV.

“I am deeply convinced that it is our Western partners, first and foremost of course the United States, who are responsible for the situation.”

Some U.S. officials argue the United States must act more forcefully in Syria or risk losing what influence it still has over moderate rebels and its Arab, Kurdish and Turkish allies in the fight against ISIS, the officials told Reuters.

U.S. officials said they consider it unlikely that President Obama will order U.S. air strikes on Syrian government targets, and they stressed that he may not make any decisions at a planned meeting of his National Security Council.