BAGHDAD — It was just the sort of episode that observers have long worried could provoke a serious conflict: when federal police agents sought to arrest a Kurdish man last month in the city of Tuz Khurmato in the Kurdish north of the country, a gunfight ensued with security men loyal to the Kurdish regional government.

When the bullets stopped flying, a civilian bystander was dead and at least eight others were wounded.

In response, the Iraqi prime minister, Nuri Kamal al-Maliki, rushed troop reinforcements to the area, and Masoud Barzani, the president of Iraq’s semiautonomous northern Kurdish region, dispatched his own soldiers, known as the Peshmerga, and the forces remain there in a tense standoff.

Almost a year after the departure of the United States military closed a painful chapter in the histories of both nations, Iraq finds itself in a familiar position: full-blown crisis mode, this time with two standing armies, one loyal to the central government in Baghdad and the other commanded by the Kurdish regional government in the north, staring at each other through gun sights, as officials in Baghdad, including American diplomats and an American general, try to mediate.