In the fight against Islamic State, also known as ISIS, the United States military has been battling them through drone strikes and air bombings across parts of Iraq and Syria with debatable results. However, ISIS has taken the fight to an American base in Iraq for the first time on Sunday.

According to a report from the Iraqi website Shafaq News, the clash took place near Ein al-Asad in the Anbar province. The U.S. troops were armed with "light and medium weapons" and, alongside the Iraqi army, managed to inflict casualties against ISIS militants in a two-hour gun battle, according to Col. Salam Nazim of the Iraqi army.

"US forces intervened because of ISIS started to come near the base, which they are stationed in so out of self-defense," said Sheikh Mahmud Nimrawi, a prominent tribal leader.

Nimrawi added that "We have made progress in (the) al-Dolab area, in which ISIS has withdrawn from." Interestingly, he noted that the battles "involved a private American force."

According to an article posted in the Inquisitr, Sunday's incident was the first time U.S. troops clashed with ISIS forces on the ground in Iraq.

The base housed about 100 U.S. military advisers. A field commander in the Iraqi army told Shafaq News that the Americans also used "F-18" fighter jets in their ground encounter with ISIS, causing the militants to retreat from the al-Dolab area.

According to Corey Charlton of The Daily Mail, ISIS launched the surprise attack against U.S. forces just after midnight in an attempt to overrun the Iraqi military base. ISIS suffered an unknown number of casualties.

"Ein al-Asad came under repeated attack by ISIS troops in October," Charlton wrote. "However, now bolstered by the U.S. assistance, it poses a much more formidable target."

Charlton added that Ein al-Asad was the largest air base located within Iraq's Anbar province during the Iraq War.

"Although it scaled down in size following the conclusion of the war, it remains in use by the Iraq Army and is located deep within the remote areas on the front line against ISIS," Charlton wrote.

According to The Daily Mail, President Barack Obama authorized air strikes in Iraq earlier this summer, citing the duty to protect an impending massacre of Yazidis by ISIS militants.

The Inquisitr reported that the United States has led a series of air strikes against ISIS positions in Iraq and Syria for several weeks in order to cripple the militant group's ability to move across the region and coordinate attacks.

ISIS has previously responded to American airstrikes by executing Western hostages and called for attacking American interests, according to the Inquisitr.