-- The United States plans to send more than 1,000 Marines to Afghanistan soon, a U.S. military official told CNN on Thursday.

The Marines will support the expansion of security efforts in southern Afghanistan, and they will be on the ground for only a few months, the official said.

"We intend to keep the pressure on the Taliban throughout the winter and take advantage of the security gains already achieved," the official said.

The Marines are headed to the Kandahar and Helmand provinces in the south, which have long been major fronts in the war against the Taliban.

A Pentagon spokeswoman told CNN there are about 97,000 U.S. service members deployed to Afghanistan. There are about 21,500 Marines in the country at present, the Marines told CNN.