Al Qaeda-linked jihadists struck back against rival rebels in eastern and northern Syria on Friday after a week of internecine fighting among opponents of President Bashar al-Assad in which 500 people have been killed, a monitoring group said.

With less than two weeks to go before what is hoped will be the first peace talks between the opposition and Assad’s government, disparate opposition groups met for the first time in the Spanish city of Cordoba. They agreed to work together but did not agree who, if any of them, should attend the peace talks.

Nearly three years into a conflict that has driven a quarter of Syrians from their homes and killed more than 130,000 people, the opposition to Assad is fragmenting. […]