A senior US defense official says the Pentagon is considering sending more military advisors to Iraq.

Their role would be to help determine future course of action for the US, based in part on the impact of several days of targeted airstrikes on the Islamic extremist fighters and how that has affected Kurdish forces opposing them in northern Iraq.

The defense official spoke on condition of anonymity because no decisions about expanding the advisor team have been made.

The Pentagon already has 250 military personnel in Iraq in advisory roles. About 90 are studying the strength of the Islamic State militant group's fighters and the Iraqi government forces, and another 160 are advising Iraqi forces on military operations.