Any extension of those measures into the rest of the country, known as the Red Zone, could quickly turn into armed confrontation. Westerners are wary of Interior Ministry checkpoints, some of which have been fake, as well as of ministry units, which are sometimes militia-controlled and have been implicated in sectarian killings. Western convoys routinely have to choose between the risk of stopping and the risk of accelerating past what appear to be official Iraqi forces.

Image Interior Minister Jawad al-Bolani said Iraqi forces would ensure that new licensing rules were being observed. Credit... Yasser al-Zayyat/Agence France-Presse

And because Western convoys run by private security companies are often protecting senior American civilian and military officials, the Iraqi government’s struggle with the companies has in some cases become a sort of proxy tug-of-war with the United States.

That dynamic was laid bare in the weeks immediately after the shooting on Sept. 16 in Nisour Square in Baghdad. The Iraqi government at first suggested that it would ban Blackwater, which has a contract to protect American diplomats, from working in Iraq. But the government was embarrassed when it discovered that its legal options were limited, and the United States — after placing a few new restrictions on the company — quickly sent it back onto the streets.

Based on its own investigation, the Iraqi government has concluded that the Blackwater guards who opened fire committed murder. An American investigation led by the F.B.I. has not yet publicly announced any results.

The outlines of a struggle for primacy on the streets also seem apparent in what the Interior Ministry says is a decision to insist that weapons carried by members of Shiite-controlled militias that protect certain neighborhoods must also be registered. Asked about the vast areas of Baghdad patrolled by the powerful Mahdi Army, which was founded by the radical Shiite cleric Moktada al-Sadr, General Khalaf said that it too would be challenged.

“In the near future there is a campaign that will happen,” General Khalaf said. “We are delaying this campaign until we finish this database.”