BEIRUT — The death toll from a suspected chemical attack on a northern Syrian town rose to 72 on Wednesday as activists and rescue workers found more terrified survivors hiding in shelters near the site of the harrowing assault, one of the deadliest in Syria’s civil war.

According to a Syrian opposition group, renewed airstrikes hit the town of Khan Sheikhoun a day after the attack that the Trump administration has blamed on the government of President Bashar Assad, saying that his patrons, Russia and Iran, bore “great moral responsibility” for the deaths.

The Damascus and Moscow governments denied they were behind the attack. A Russian Defense Ministry statement later said the toxic agents were released when a Syrian airstrike hit a rebel arsenal.

The U.N. Security Council was to hold an emergency meeting on Wednesday in response to the strike and in Brussels, officials from 70 nations gathered for a major donors’ conference on the future of Syria and the region.

The attack on Khan Sheikhoun killed dozens of people on Tuesday, leaving residents gasping for breath and convulsing in the streets and overcrowded hospitals. Videos from the scene showed volunteer medics using fire hoses to wash the chemicals from victims’ bodies. Haunting images of lifeless children piled in heaps reflected the magnitude of the attack, which was reminiscent of a 2013 chemical assault that left hundreds dead and was the worst in the country’s ruinous six-year conflict.