ERBIL, Iraq — Gov. Atheel al-Nujaifi wants his province back.

Since early June, when jihadist militants swept into Nineveh Province in northern Iraq and seized control of its capital, Mosul, Mr. Nujaifi has been a man without a home.

As Iraqi forces and various militias, backed by American airstrikes, have sought to beat back fighters calling themselves the Islamic State, Mr. Nujaifi has pursued his own military response, narrowly tailored toward reclaiming Mosul. He is trying to assemble a 3,000-person militia of mostly Sunni Muslims from Nineveh Province to deploy against the militant group, also known as ISIS.

“We want to give a new image to the people: that Mosul will fight ISIS with people mainly from Mosul,” he said. “The people will not accept a return of the Iraqi Army.”

There are countless hurdles to this project, not least of which is that the central government in Baghdad is not likely to approve it. But however quixotic, the plan dovetails conceptually with a new national security strategy, announced by Prime Minister Haider al-Abadi last week, to create national guard forces under the authority of the nation’s provincial governors.