The Obama administration has promised "any appropriate assistance" to the Iraqi government to help deal with militant Islamist group ISIS.
The group now appears to have control of the city of Tikrit, just 100 miles from the capital Baghdad.
However the US State Department said Iraq's largest oil refinery still "remains under the control of the government".
The Foreign Secretary has been clear on the threat of Isis, but he has ruled out the prospect of any UK military involvement in the crisis.
Iraq’s foreign minister, Hoshyar Zebari, is a natural diplomat. Polite, immaculately dressed, and blessed with a great memory.
Isis has paraded military equipment in Mosul it captured from when the Iraqi army fled in what some see as a "nightmare scenario."