Militants from ISIS and Iraqi troops are locked in heavy fighting for the Baiji oil refinery and Tal Afar airport.
The clashes come after US President Obama said he would send 300 military advisors to assist the Iraqi army, but he did not authorise immediate air strikes despite a formal request made by Baghdad.
The US said that efforts to bridge sectarian divides would need to be made by the government before further military support would be given.
Pressure on Premier Nouri al-Maliki to resign is growing, but his spokesperson said he would not step back as a condition of air strikes by the US.
ISIS has surrounded the Baiji oil refinery, the largest in the country, and most of the airport in Tal Afar is also under their control.
Australia's Prime Minister Tony Abbott meanwhile said that his government is monitoring the situation and will consider sending military support if requested.