SHAQOULI, Iraq — To defend a few miles of unremarkable road in northern Iraq, flanked by farmland, the occasional factory and flyspeck hamlets and villages, the Islamic State militants seemed to spare no effort.
They loaded a Volkswagen with explosives and secreted remote-detonated bombs into the road’s median strip. They burned tires and dug large tunnels in houses, to obscure their positions. They placed crude mortar launchers on the road’s shoulder, pointed in the direction of any approaching force.
The arsenal ultimately failed to protect the militants as thousands of Kurdish soldiers known as peshmerga swept down the road Monday as part of a broader offensive to drive the militants out of Mosul. But it seemed to slow down the action Tuesday, tying up a large contingent of Iraqi soldiers for the better part of the day as they tried to clear the road and surrounding villages of booby traps, a few wearying feet at a time.
There were still 12 grueling miles left to travel before reaching the city’s outskirts.
The struggle for Mosul — which involves U.S. air power and an array of Iraqi ground forces — is the largest and most complex so far in the battle against Islamic State militants, who have been digging in for a fight. Residents who have recently fled the area and Iraqi officials with contacts inside the city say the Islamic State has been erecting concrete barricades and filling trenches with oil that can be set on fire to slow advancing forces.
“It’s going to be a tough fight and a difficult fight,” President Obama said Tuesday at a news conference with visiting Italian Prime Minister Matteo Renzi. “It is Iraqis who are doing the fighting. And they are performing effectively and bravely, and taking on significant casualties. There will be ups and downs in this process, but my expectation is that ultimately it will be successful.”
Despite the looming challenges, Iraqi and American officials have praised the early success of the operation and said that on its first day, the thousands of Kurdish and Iraqi army soldiers taking part had met their initial objectives. The offensive is a rare collaboration between the two forces, who answer to the frequently feuding governments in Baghdad and Irbil, the capital of the semiautonomous Kurdish region.
On Tuesday, the Iraqi military’s 9th armored division also said it had advanced, breaking into the district of Hamdaniya and besieging the Christian town of Qaraqosh, about 10 miles southeast of the outskirts of Mosul, according to the commander, Lt. Gen. Qassim al-Maliki. “We will storm it any minute,” he said Tuesday evening.
Iraqi army and police forces are also advancing from Qayyarah air base south of the city. Col. Abdel Rahman al-Khazali, a spokesman for federal police, said his forces had reached Shora, 20 miles south of Mosul.
But Kurdish commanders also said they had delayed a planned push toward the Islamic State-held town of Bashiqa, northeast of Mosul, for reasons that remained unclear. Several of the commanders blamed the Iraqi army, saying it had failed to immediately take up defensive positions in territory that was captured on Monday.
Brig. Gen. Haider al-Obeidi, an Iraqi special forces commander, said the Iraqi forces were “waiting for the peshmerga to finish their job.”
“We are waiting for them to reach the areas they were supposed to reach under the military plan, so that we can move,” he said.
Whatever the reason, the consequences of the delay were immediately apparent: Militants around Bashiqa repeatedly fired mortars at a peshmerga base Tuesday, soldiers at the base said.
When it does come time to clear the town, the militants are likely to mount a more formidable defense than they did around the much smaller villages on Monday, according to Lt. Col. Sanger Abubaker, the commander of a Kurdish support unit.
“For sure, there will be resistance,” he said. The town, with its proximity to Mosul, “is important to them,” he added.
The Islamic State claimed to have carried out 12 suicide attacks on the first day of the offensive, according to its affiliated news agency, Amaq. Jabbar Yawar, a spokesman for the peshmerga forces, said eight Kurdish soldiers were killed Monday and 16 injured.
Three peshmerga soldiers, including two in Shaqouli, were killed while trying to detonate leftover explosive devices Tuesday, local media reported.
The determination of Islamic State fighters to hold territory came into sharp focus Tuesday, on the stretch of road the Kurds had captured. Near the village of Sheikh Amir, parts of the two-lane road had been gutted by burrowed explosives. Mortar shells sat in a guardhouse outside the village, near smoldering tires that had blackened a small field.
Mohamed Emad, a de-miner with Iraq’s counterterrorism forces, scoured the sides of the road for hidden bombs, looking for clues in the texture of the dirt. By lunchtime, he had uncovered at least 30, he said, as he fiddled with a remote detonator from one of the explosive devices.
Nearby, a crumpled car sat at the side of the road, next to some freshly dug earth. Dana Dara, a 29-year-old Kurdish soldier, narrated the tableau, saying that five Islamic State militants had been inside the car, which was loaded with explosives, when the peshmerga fighters stopped it with a rocket-propelled grenade.
The soldiers moved the car off the road, and dug a grave right beside it, for the five men from the Islamic State.
Morris reported from Irbil. Aaso Ameen Shwan in Shaqouli, Mustafa Salim in Irbil and Karen DeYoung in Washington contributed to this report.