Maliki Iraq Terrorism
Iraq's Prime Minister Nuuri al-MalikiReuters

Iraqi prime minister Nouri al-Maliki has called for national unity in the face of the advance of Islamist-led Sunni militants.

Speaking of the swift breakthrough of the Islamic State of Iraq and the Levant (Isis) and other Sunni allies in Diyala and Salahuddin provinces, Maliki expressed optimism that "Iraqi people will not be defeated".

"The country has suffered setback, but not every setback is a defeat. It has allowed Iraq to recover national unity," he said in a televised address.

Isis fighters have invaded Iraq's biggest oil refinery in Baiji and are now controlling 75% of the facility. A defiant Maliki also appealed to volunteers to take arms against the Sunni militants. "You will be the backbone of a new Iraq," he said.

However, Maliki's call for national unity is unlikely to have any effect as the Shia leader has been accused over the years of centralising power within his inner circle and disenfranchising Sunnis out of political power. His increased authoritarian rule has fuelled the Sunni insurgency, according to experts.

The latest development came as Saudi foreign minister Saud bin Faisal warned that Iraq faced the risk of civil war.