BAGHDAD — Al-Qaida-inspired militants who seized large parts of the Iraqi city of Mosul moved to reassure nervous locals on Wednesday as top officials pledged to drive the insurgents out.

Prime Minister Nouri al-Maliki said the massive security failure in Sunni-dominated Ninevah province that allowed militants aligned with the Islamic State of Iraq and the Levant to seize the country’s second largest city was the result of a “conspiracy,” and that those members of the security forces who fled the fighting rather than standing up to the militants should be punished.

He stopped short of assigning direct blame, however, choosing to focus instead on plans to fight back — without detailing the specifics.

“Today, the important thing is that we are working to solve the situation,” a stern-faced al-Maliki said. “We are making preparations and we are regrouping the armed forces that are in charge of clearing Ninevah from those terrorists.”

The stunning assault by the al-Qaida-inspired group saw black banner-waving insurgents raid government buildings, push out security forces and capture military vehicles as residents fled for their lives.

Mosul is the capital of Ninevah province. It and the neighboring Sunni-dominated province of Anbar share a long and porous border with Syria, where the Islamic State is also active.

Ninevah governor Atheel al-Nujaifi told reporters that “Mosul is capable of getting back on its feet and getting rid of all the outsiders,” and said authorities planned to mobilize residents into popular militias that would play a role in retaking the city.

There were no immediate estimates on how many people were killed in the assault but the rampage sent an estimated 500,000 people fleeing from the city and surrounding areas, according to the International Organization for Migration.

Some simply crossed to the eastern bank of the Tigris River to avoid the worst of the fighting, while others made their way to the Ninevah countryside or sought refuge in the nearby semiautonomous Kurdish region.

Getting into that area has grown trickier, however, with migrants without family members already in the enclave needing to secure permission from Kurdish authorities, according to the IOM.