Despite mounting pressure to step aside, Nouri al-Maliki vowed Friday he will not abandon his bid for another term as prime minister of Iraq, pledging to stay on until the Sunni militants who have overrun much of the country are defeated.

The sharp words are certain to prolong the political impasse gripping Iraq, which is facing urgent demands for a new government that can hold the nation together in the face of an onslaught by militants from the Islamic State of Iraq and Syria that threatens to cleave it in three along ethnic and sectarian lines.

ISIS fighters have swept across much of northern and western Iraq since last month in an offensive fuelled in part by grievances among the country's Sunni Muslim minority with al-Maliki and his Shia-led government.

Al-Maliki, a Shiite who has been prime minister since 2006, has been accused by former allies and others of monopolizing power and contributing to the crisis by failing to promote reconciliation with Sunnis.

'I will never give up the nomination for the post of prime minister.'- Nourial al-Maliki

The United States has urged the formation of a more inclusive government but has not explicitly called for al-Maliki to bow out.

In what has been seen as a rebuke of al-Maliki, Iraq's top Shiite cleric, Ayatollah Ali al-Sistani, has pressed lawmakers to quickly form a new government that can confront the militant threat and unite the country. Lawmakers failed in their first session of parliament on Tuesday to make any progress.

On Friday, al-Sistani lamented the inability of political leaders to agree on a new prime minister and urged them to redouble their efforts, a cleric who represents him told worshippers in a sermon in the holy city of Karbala.

Al-Maliki's State of Law coalition won the most parliamentary seats in April elections, which would traditionally make him the leading candidate to head a new government. But al-Maliki failed to gain a majority in the legislature, meaning he needs allies to form a government. That has set the stage for intense wrangling over the makeup of a coalition — and, above all, who will be prime minister.

Al-Maliki made clear on Friday his determination to stay on for a third consecutive term — or at least until he has crushed the insurgency

"I will never give up the nomination for the post of prime minister," he said in a statement issued by his office.

He framed the debate over his future in democratic terms, reminding Iraqis that the voters handed his bloc the most seats in parliament, and declaring that he must "stand by them during this crisis that Iraq is passing through."

Al-Maliki said that to pull out now "while facing terrorist organizations that are against Islam and humanity would show weakness instead of carrying out my legitimate, national and moral responsibility."

"I have vowed to God that I will continue to fight by the side of our armed forces and volunteers until we defeat the enemies of Iraq and its people," he said.

Fighting reported at refinery

In another development, a spokesman for the country's counterterrorism forces said Friday government airstrikes have targeted a group of Sunni militants trying to overrun the country's largest oil refinery, and claims as many as 30 insurgents have been killed.

Sabah al-Nuaman said a government plane targeted about eight vehicles attacking military forces defending the Beiji oil refinery north of Baghdad early Friday. Fighters from the Islamic State of Iraq and Syria extremist group have been trying to capture the Beiji facility from some two weeks.

Al-Nuaman also says a helicopter gunship hit a house in the town of Qaim near the Syrian border where a gathering of the jihadi group's local leaders was taking place. He says there were several casualties, but did not have a concrete figure.

An official in the Anbar province operational command confirmed the Qaim airstrike.