KABUL (Reuters) - U.S. Army General John Campbell stepped down as commander of the NATO-led coalition in Afghanistan on Wednesday, capping an 18-month tenure that saw the alliance transition from regular combat to a training-focused mission as war continued to rage.
The incoming commander, General John Nicholson, will inherit a conflict that is testing Afghan security forces and the roughly 13,000 international troops who remain, with insurgents contesting or controlling as much as a third of Afghanistan.
Since Campbell took command of both coalition troops and U.S. counterterrorism operations in August 2014, Taliban militants have made gains in several provinces, Islamic State has established a nascent presence, and casualties have increased among both Afghan security forces and civilians.
The Taliban are seeking to topple the Western-backed government in Kabul and reimpose strict Islamic rule 15 years after they were ousted from power.
"No doubt this has been a challenging and difficult time in our campaign," Campbell told Afghan and international dignitaries gathered at the coalition's headquarters in Kabul.
"The confluence of changes in the environment reminds us that there are challenges ahead, but that together we can face and overcome them."
Taliban gains, including their brief capture of the northern city of Kunduz last year, led Campbell to recommend keeping more American troops. President Barack Obama abandoned plans in October to withdraw all U.S. forces, instead opting to leave thousands in Afghanistan at least until 2017.
Nicholson brings long experience in Afghanistan, having already spent three-and-a-half years deployed to some of the most contested areas.
In his first visit outside of Kabul since his arrival to assume his new command, Nicholson said he had traveled to Helmand province to try to reassure Afghan leaders there who have faced some of the most serious fighting.
"The United States is committed to an enduring relationship with Afghanistan," he said at Wednesday's ceremony. "We are with you."
Campbell reiterated his call for international leaders to remain flexible and to base any decisions on troop levels on conditions on the ground to prevent a repeat of some of the worst violence in 2015.
Afghan and coalition leaders praised Campbell, a 41-year veteran of the U.S. military, but the outgoing commander's tenure was not without controversy.
Besides the deteriorating security situation, he faced sharp criticism over an American air strike on a Doctors Without Borders hospital in Kunduz in October that killed at least 42 medical staff, patients, and caretakers. The full results of an investigation into the strike have yet to be released.
Reporting by Josh Smith; Editing by Nick Macfie