KANDAHAR AIRFIELD, Afghanistan — NATO officials formally took control of military operations in southern Afghanistan on Monday, pledging that their members will remain in the country until security is established.

“We will not leave until the Afghan people tell us that our job is complete,” said British Lt. Gen. David Richards, commander of NATO’s International Security Assistance Force. “We recognize that much remains to be done, and we do not underestimate the significant task to which we have committed ourselves.”

Richards’ comments came at a formal ceremony held inside an airstrip hangar, and the festivities were interrupted several times by the sound of helicopters leaving and returning from missions throughout this volatile region.

The mission is considered the most dangerous and challenging in NATO’s 57-year history. It coincides with the deadliest upsurge in fighting in Afghanistan since late 2001, which has killed hundreds of people — mostly militants — since May.

NATO conducted aerial combat operations during the wars in Bosnia and Kosovo in the 1990s, but has yet to conduct major ground combat operations since being founded in 1949 as a deterrent against the Soviet bloc.

U.S. forces have commanded all operations in the southern quarter of the country since Operation Enduring Freedom began in 2001.

The south also has been the focus of some of the harshest fighting in the country in recent weeks, after U.S. and coalition forces launched Operation Mountain Thrust to disrupt established enemy strongholds in the region.

The six provinces handed over on Monday make up the third region to transfer authority, with the entire country scheduled to fall under NATO control by the end of the year.

The new international military force will include troops from nine countries, including Afghanistan and the United States.

Richards said NATO’s focus in the south will lean more heavily on redevelopment and economic aid, but he said the command shift will not produce any gap in those military operations.

Lt. Gen. Karl Eikenberry, commander of Combined Forces Command Afghanistan, said U.S. troops will remain in the region to continue those fights, now joined with thousands more international troops under the ISAF.

“The war on terrorism began here in Afghanistan, and it continues today,” he said. “We must never forget that. The international community must remain fully engaged, and I can assure you that the United States will fulfill its pledge to the Afghan people.”

About 2,700 U.S. troops will remain operating in the south. NATO officials say they will have a total of about 9,000 troops at their disposal, almost three times what the region had last year. According to the London Daily Telegraph, it is the first time American troops have been under the command of a British general since World War II.

Richards could not say when NATO forces might be able to draw down those troop levels.

He said he expects forces will need three to six months to determine whether they have effectively neutralized Taliban fighters in the region, and speculated that military operations will likely continue in the region for three to five more years.

Afghan Minister of Defense Abdul Rahim Wardak praised both the United States and NATO for their commitment to his country.

“We are all struggling and fighting for a just cause, and I have no doubt we will prevail,” he told the assembled officials.

“Your sacrifices, your help has been highly appreciated, and we are eternally grateful. We hope one day we will be able to pay you back for this.”

The Associated Press contributed to this report.

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