The United States and the United Kingdom have accused the Afghan Taliban of massacring civilians as they captured a town in Kandahar province near the Pakistan border. The U.S. and U.K. embassies in Kabul both tweeted Monday that dozens of civilians were slaughtered in Spin Boldak in revenge killings that could constitute “war crimes.” The statements came as the U.S. stepped up airstrikes aimed at slowing a rapid advance by the Taliban in several Afghan provincial capitals.