Updated

Without firing a shot, Kurdish militiamen moved closer Saturday to the key prize of the north -- Kirkuk and its oil fields -- after Iraqi forces staged a sudden withdrawal to possibly plug defenses targeted by U.S. airstrikes.

The extent of the aerial barrage around the northern centers of Kirkuk and Mosul is not fully known, although explosions and heavy anti-aircraft fire could be heard from Kirkuk. But Kurdish commanders interpreted the latest retrenching of Iraqi forces toward Kirkuk as evidence that the daily attacks had taken a serious toll and that Saddam Hussein needed to solidify the lines.

"They are getting ready for a last stand," said the leader of a front line unit, Farhad Yunus Ahmad, as he crouched behind a knoll and scanned for signs of Iraqi troops along the main road linking Irbil in the Western-protected Kurdish region to Kirkuk.

Iraqi soldiers fell back at least 12 miles late Friday to apparently regroup near Perdeh -- also known as Altun Kupri -- about 27 miles from Kirkuk, which is Iraq's No. 2 oil producing region. Iraqi troops made a similar pullback east of Kirkuk on Thursday.

Perdeh's centerpiece is an important bridge over the Little Zab River. Bypassing the bridge would require coalition forces to make difficult and potentially dangerous detours through rolling hills where Iraqis could stage guerrilla-style ambushes or fire from higher ground.

But there are no orders yet to open a northern ground offensive.

Meanwhile Saturday, Kurdish and U.S. special forces in northeast Iraq targeted Ansar al-Islam extremists, Islamic militants with alleged ties to al-Qaida terrorists. Heavy machine gunfire and bombardments were reported close to Halabja, near the Ansar positions.

Barham Salih, prime minister of the Sulaymaniyah-based Kurdish government, called the attack a "very serious blow" against terrorism, saying many of those killed were Arabs who had fought and trained in Afghanistan.

The Pentagon has only about 1,200 paratroopers and some special forces at its disposal in the Kurdish autonomous region -- a force too small to directly challenge Saddam's military, although reinforcements and heavier firepower are expected. Kurdish leaders, meanwhile, have pledged not to launch any independent attacks.

The Kurdish militia force in the Irbil area is about 5,000; in the entire enclave there are about 70,000 guerrilla militiamen known as peshmergas -- literally, "those who face death."

Kirkuk would be one of the main goals of a northern push. U.S.-led forces hope to avoid any damage to the vital oil fields. Kurds view the city as an integral part of their ethnic territory and insist on the return of thousands of Kurds driven out by Saddam's regime.

The peshmergas advanced cautiously at dawn into the territory opened by the overnight withdrawal. For many, it was their first look at land held by Baghdad since a failed 1991 Kurdish uprising after the Gulf War.

The road appeared to be mined in places. Along one stretch, it was blocked by long metal bars and earthen mounds.

At first, some Kurds feared the pullout could be a trap by Iraqi commandos. But worries faded as each crest revealed a panorama of empty grazing land and abandoned installations.

Iraqi soldiers left behind cinderblock bunkers, sandbags and barbed wire barricades. But no weapons or strategic information were found, Kurdish fighters said. On Friday east of Kirkuk, Kurdish militiamen said they'd found gas masks and vials of the nerve gas antidote atropine in the headquarters of Saddam's Baath Party in Qala Hanjir.

Along the Irbil-Kirkuk road, Kurds planted the yellow flag of the Kurdistan Democratic Party -- one of the two main Kurdish factions -- atop a former Iraqi observation hill overlooking the abandoned village of Shehan surrounded by lush pastures dotted with yellow and violet wildflowers.

"I used to live on a farm over there," said fighter Hamza Ali, pointing to a cluster of broken stone buildings outside the village. "The Iraqi army destroyed everything. It's sad to be back here and see my village this way."

Tracks in the mud suggested the Iraqis had some tanks in the area recently.

In a foxhole, an Iraqi soldier left an empty pack of Al-Rashid cigarettes with some pencil doodles on the inside cover. The Iraqi-made brand claims to be "the finest Virginia filter cigarettes."

The Kurdish fighters -- in mismatched uniforms and munching on wild celery -- posed for snapshots. Overhead, the contrails of U.S. warplanes left white cat claw streaks in the cloudless sky. On the horizon: the dark smoke from a bombing strike in the direction of Kirkuk.

"This move by the Iraqi forces must mean only one thing: Saddam's government is using whatever it has left to try to defend Kirkuk," said a Kurdish special forces chief, Nazim Harki. "And we are another step closer to Kirkuk."