The secret Iranian programs are a rare instance in which Iran and the United States share a near-term goal: countering the Islamic State in Iraq and Syria, or ISIS, the Sunni militants who have seized towns and cities in a blitzkrieg across western and northern Iraq. But even as the two nations provide military support to the embattled government of Prime Minister Nuri Kamal al-Maliki, they are watching each other's actions warily as they jostle for influence in the region.

Senior American officials emphasized that the parallel efforts were not coordinated, and in an appearance at NATO headquarters here on Wednesday, Secretary of State John Kerry highlighted some of the potential risks.