(CNN) -- A U.S. Marine unit that had been fighting insurgents in a volatile region of southern Afghanistan has turned over control of the area to Afghan and British forces, NATO's International Security Assistance Force said Monday.
The 2,400-strong U.S. 24th Marine Expeditionary Unit had been overseeing operations in Helmand province's northern Garmsir district -- long "a staging and transit area" for militants, ISAF said.
The handover comes as the U.S. military has been studying the deployment of more U.S. troops for Afghanistan, where recently more than 33,000 Americans have been serving under NATO-led and coalition commands.
The troops held a handover ceremony Monday, and now the Marines are getting ready to return to Camp Lejeune in North Carolina.
The Marines began an operation in late April and for 35 days worked to clear parts of Garmsir, battling in 170 engagements and causing more than 400 "severe insurgent casualties," ISAF said. There were no civilian casualties, it said.
"Through the capture of a series of identified enemy strong points and defensive positions, Marines opened the previously denied routes through Garmsir district to the economically vital Helmand green zone," ISAF said.
The Marines then "transitioned to stability operations," working with British forces to open a Joint Civil Military Operations Center" and paying out battle-damage reparations, it said.
"Through countless patrols, which later became joint patrols as the Afghan forces flowed into the area, the Marines maintained a stable environment -- one which enabled the Afghan citizens to return to the homes they had been displaced from up to two years earlier by the insurgents," it said.