But Kirkuk’s minorities are already on edge. “We are scared now for our city because after 10 years we have turned back to the zero point,” said Mijbel Adbulrahman, a 52-year-old Arab. “We have turned back to the conflict between Arabs and Kurds.”

Even before this crisis, the Kurds, with their own security forces, diplomats and a booming economy, were steadily moving toward independence by securing deals with Turkey and international companies to pump oil out of the region, without the approval of Baghdad. Baghdad and the United States regarded those deals as illegal, contending that any oil within Iraq belongs to the nation, not to a part of it.

But the Kurds pushed on anyway, and two tanker ships filled with Kurdish oil are sailing around the Mediterranean Sea, having left in recent weeks from a port in Turkey, but with nowhere to dock because of threats of legal action by Washington and Baghdad.

Before the seizure of Mosul, preventing that oil from hitting international markets had been a centerpiece of Washington’s Iraq policy for the past two years, and American officials had believed that the sale of Kurdish oil, without Baghdad getting its cut, was a greater threat to the cohesion of Iraq than surging militants in Syria who had their sights set on bringing the fight to this country.

Now, however, Baghdad is focused more on the Kurds’ renowned battlefield prowess and how the pesh merga can help turn back the militants’ thrust. Falih al-Fayadh, Mr. Maliki’s national security adviser, said in a news conference recently that the central government was working with the Kurds, calling the fight against the militants a “joint battle.”

But Jabar Yawar, the spokesman for the pesh merga, said: “It is all talk. We have a relationship, but there is no cooperation.” The Kurds’ interests lie in expanding their territory to take in all the predominantly Kurdish areas of Iraq, while mostly keeping out of the larger fight.

Mr. Yawar laid out a map that showed the expanding positions of Kurdish forces in Iraq, across an area stretching from the Syrian border in the west to the Iranian border in the east. The territory along a blue line, much of which the Kurds previously controlled jointly with the Iraqi Army, is now theirs, after Iraqi soldiers either deserted or fled south toward Baghdad.