Syria peace talks ran into trouble on Monday, with the U.N. mediator saying the opposition has suspended its formal participation in the indirect discussions with President Bashar Assad’s government to protest “worrisome” new violence, especially near the northern city of Aleppo, and rising concerns about the humanitarian situation.

Staffan de Mistura, the U.N envoy for Syria, said he will press on with the talks despite the suspension by the opposition High Negotiations Committee. The HNC said it would no longer attend meetings at the U.N. office in Geneva that has hosted weeks of on-and-off peace talks aimed ultimately at ending the country’s devastating five-year war.

The HNC delegation will remain at their hotel in Geneva, and de Mistura said he will continue “technical” discussions with its envoys by phone or off-site in hopes of firming up a blueprint for a political transition in Syria. He said he would “take stock” of progress toward that goal on Friday. […]