The U.S. demanded on Thursday that Russia immediately halt its bombing campaign in Syria after a bitter breakdown in peace talks exposed the deep rift between world powers aiming to end the five-year conflict.

On the ground, nearly 40,000 people have fled an offensive this week by President Bashar Al-Assad’s regime north of the city of Aleppo, according to the Syrian Observatory for Human Rights monitor. Mr. Assad’s forces also entered two Shia villages that were under siege by rebels.

U.S. Secretary of State John Kerry warned Moscow to halt its bombing of the Syrian opposition in what he said was a “robust” phone call with Russian counterpart Sergei Lavrov. “We discussed, and we agreed, that we need to discuss how to implement the ceasefire,” he said, adding he and Mr. Lavrov would speak again later Thursday or on Friday.

Meanwhile, aconference of donor nations raised $11 billion for Syrian humanitarian needs over the next four years, British Prime Minister David Cameron said on Thursday as the event in London drew to a close. Mr. Cameron told a news conference that donors had pledged $6 billion for this year alone, and a further $5 billion to be spent by 2020.(Reuters)