The Iraqi prime minister's televised address to the nation was his first public statement since US President Barack Obama challenged him last week to create a more inclusive government or risk his country descending into sectarian civil war.
US officials believe the leadership in Baghdad should seek to draw Sunni support away from the militants led by al Qaeda breakaway group the Islamic State of Iraq and the Levant (Isis), which has seized a chunk of north-western Iraq and seeks to carve out a purist Islamic enclave across both sides of the country's border with Syria.
The insurgency has drawn support from disaffected Iraqi Sunnis who are angry over perceived mistreatment and random detentions by the Shiite- led government.
The crisis has drawn the US back to Iraq, nearly three years after the Americans withdrew from the country. Dozens of newly arrived US military advisers and special operations forces have started assessing the Iraqi forces in an effort to strengthen Baghdad's ability to confront the insurgency.
In the face of militant advances that have virtually erased Iraq's western border with Syria and captured territory on the frontier with Jordan, Mr Maliki's focus has been the defence of Baghdad, a majority Shiite city of seven million fraught with growing tension.
The city's Shiites fear they could be massacred and the revered al Kazimiyah shrine destroyed if Isis fighters capture Baghdad. Sunni residents also fear the extremists, as well as Shiite militiamen in the city, who they worry could turn against them.
Several politicians, including Ayad Allawi, a secular Shiite who has been named as a possible contender to replace Mr Maliki, have called on him to step down and form an interim government that could provide leadership until a more permanent solution can be found.
However, Mr Maliki insisted the political process must be allowed to proceed following recent national elections in which his bloc won the largest share of parliament seats.
"The call to form a national salvation government represents a coup against the constitution and the political process," he said, adding that "rebels against the constitution" - a thinly veiled reference to Sunni rivals - posed a more serious danger to Iraq than the militants.
He called on "political forces" to close ranks in the face of the growing threat by insurgents, but took no concrete steps to meet US demands for greater inclusion of minority Sunnis.
"We desperately need to take a comprehensive national stand to defeat terrorism, which is seeking to destroy our gains of democracy and freedom, set our differences aside and join efforts," said Mr Maliki.
"The danger facing Iraq requires all political groups to reconcile on the basis and principles of our constitutional democracy."
In fighting yesterday, Sunni militants launched a dawn raid on a key Iraqi oil refinery they have been trying to take for days, but security forces fought them back.