The Iraqi army is struggling in its efforts to retake Mosul in northern Iraq from the Islamic State (ISIS/ISIL), revealed Reuters on Friday, the second day of an offensive described as the beginning of a broader campaign.

This revelation comes a day after The Associated Press (AP) learned from U.S. officials, who spoke on condition of anonymity, that:

The American combat role in Iraq appeared to expand on Thursday as U.S. Marines operating from a small outpost provided targeting assistance and artillery fire to support Iraqi troops inching forward to retake Mosul from Islamic State militants.

Citing the commander of the Iraqi Kurdistan Regional Government’s (KRG) peshmerga forces, Najat Ali, and an Iraqi army source who is taking part in the offensive, Reuters notes that the Iraqi army launched the assault to recapture Mosul at dawn on Thursday, with the support of KRG forces and the U.S.-led coalition.

The Iraqi forces have reportedly been able to seize three villages in the Makhmour area south of Mosul.

However, Reuters learned from the Iraqi army source that U.S.-backed forces “were preparing to attack another village on Friday but were being held up because the militants had rigged streets and buildings with explosives.”

“The mining has slightly slowed down the army,” the anonymous source told Reuters.

ISIS had also used suicide car bombs, according to the peshmerga commander and the Iraqi army source.

“Thousands of Iraqi troops have deployed to the north in recent weeks, setting up base alongside the Kurdish peshmerga and U.S. forces in Makhmour, which is set to be a key launchpad for any future offensive on Mosul, around 60 km [about 37 miles] north,” reports Reuters.

Kurdish news outlet NRT TV quotes Noful al-Agoub, the governor of Iraq’s northern Nineveh province where the offensive is taken place, as saying:

American land troops did not take part in the offensive, but air support and air strikes against Daesh [Arabic name for ISIS] by the [U.S.-led] coalition have helped control the situation on the ground and facilitate the entry of Hashd forces and troops of the 15th [Iraqi army] division.

“Hashd,” which is Arabic for “mobilization,” refers to the Shiite militias in Iraq, many of which are backed by Iran.

An anonymous senior U.S. official is quoted by AP as saying, “The [American] Marines fired illumination rounds to help the Iraqi forces locate [ISIS] fighters, and also fired artillery rounds in support of the operation, as Iraqi troops took control of several villages on the outskirts of Makhmour, southeast of Mosul.”

Earlier this week, the Pentagon confirmed that the Marine outpost, dubbed Fire Base Bell, had been established in Iraq. It is the first outpost erected in Iraq by the United States since it returned troops to Iraq in 2014.

U.S. military officials have “insisted that the nearly 200 Marines were only there to provide security for Iraqi forces and U.S. advisers at the nearby Iraqi base in Makhmour,” reports AP.

“However, the use of illumination rounds and artillery to support the forward advance of the Iraqi troops appeared to expand the Marines’ role from purely security to more direct combat action, although the Marines were not on the front lines with the Iraqis,” adds the report.