The top U.S. commander in Afghanistan says about 10 percent of the country's population is controlled by the Taliban and at least another 20 percent is being contested by the insurgents and the Afghan forces.

Army Gen. John Nicholson tells Pentagon reporters that there are up to 1,300 Islamic State militants in Syria, mainly in the east. And he said Islamic State leaders in Syria provide money, command-and-control guidance and communications support to their militants in Afghanistan. But he says U.S. and Afghan military operations have targeted the group, killing many leaders and members, so they are in fewer Afghan districts now than they were months ago.

Nicholson says he's concerned about Afghan troop casualties, saying many are at small checkpoints where forces are not well-equipped or well-trained.