The Pentagon will likely send more troops into Iraq in the coming weeks to support operations against Islamic State militants in Mosul, the military's top officer said Friday.

Marine Corps Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said that he and Defense Secretary Ash Carter will recommend to the White House expanding the U.S military footprint there as Iraqi forces undertake a complicated, large-scale offensive to oust ISIS from its stronghold in the country's north .

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Currently, the U.S. force level in Iraq is officially capped at 3,870. But privately, defense officials say the real number is closer to 5,000 when accounting for troops considered to be there on "temporary" deployment.

Among those temporary troops was Marine Staff Sgt. Louis Cardin, of Temecula, California, who was killed March 19 in an ISIS rocket on Fire Base Bell in northern Iraq.

Before Cardin’s death, military officials had not publicly acknowledged the fire base's existence. It was created several days before the fatal attack, near the forward line of troops and the Iraqi army's division headquarters in the northern Iraqi town of Makhmour.

Dunford said the decision to send more U.S. troops would be "focused on what is it we need to do to maintain momentum in the campaign and what specifically do we need to do to enable operations in Mosul."

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In December, Carter told Congress that the Obama administration was willing send additional combat advisers and attack helicopters for close air support if the Iraqis made an official request for such additional assistance. The Iraqi government declined that military support, mainly because many powerful Shiite factions in Baghdad oppose expanding the U.S. military presence.

The Iraqi army on Thursday announced the launch of an offensive to seize several villages south of Mosul, operations aimed at cutting off key supply lines to ISIS territory south and east of Mosul.

Marines at Fire Base Bell provided artillery fire support for the offensive operations, military officials said.

U.S. Marines with Task Force Spartan, 26th Marine Expeditionary Unit (MEU), on Fire Base Bell, Iraq, fire an M777A2 Howitzer at an ISIS infiltration route March 18, 2016. The Marines fired upon the enemy infiltration routes in order to disrupt their freedom of movement and ability to attack Kurdish and Peshmerga forces. Operation Inherent Resolve is an international U.S. led coalition military operation created as part of a comprehensive strategy to degrade and defeat the Islamic State of Iraq and the Levant. (U.S. Marine Corps photo by Cpl. Andre Dakis/Released)

U.S. Marines operating at Firebase Bell fire an M777A2 Howitzer at an ISIS infiltration route March 18.

Photo Credit: Cpl. Andre Dakis/Marine Corps