"They've gone down there to assist the police zone headquarters and their leadership team with a focused train, advise and assist mission," Cook told reporters, adding "This will not be a permanent presence."
The troops will attempt to help the Afghans hold on to the city of Lashkar Gah, the southern capital of Helmand province.
Helmand province is the epicenter of Afghanistan's illegal but lucrative opium industry, which is estimated to generate $3 billion each year in one of the poorest and most corrupt countries in the world.
In an effort to cut off the illicit revenues, which help fund the Taliban insurgency, the U.S. made Helmand a focus of its troop buildup that that saw the number of U.S. forces in the country quadrupled from under 25,000 in 2008 to a peak of nearly 100,000 in 2011.
Now, a resurgent Taliban threatens to take Helmand's capital after gaining control of much of the overall territory in the province, the head of Helmand's provincial council, Kareem Atal, told The Associated Press
"Around 80 percent of the province is under the control of the insurgents," he said, noting that battles were taking place "on several fronts."
"There are a number of districts that the government claims are under their control, but the government is only present in the district administrative center and all around are under the control of the insurgents," Atal added.
In 2009, approximately 20,000 U.S. Marines were based in Helmand, alongside 10,000 British troops as they tried to eliminate the insurgency, paying a heavy price. In 2010, 25 Marines were lost in one seven-month period as they took the fight to the Taliban.
Earlier this summer, the president announced he was changing his plans to draw down troops there in the face of the worsening situation, leaving more than 8,000 troops in Afghanistan beyond his time in the White House.
The Associated Press and ABC News's Jon Williams contributed to this report.