KANDAHAR: US-led forces were Saturday winding down one of their biggest offensives yet in Afghanistan, but an official said it was a mere prelude to a larger assault in the works on the Taliban bastion of Kandahar.

The two-week Operation Mushtarak ("Together") had symbolically culminated Thursday when authorities hoisted the Afghan flag in Marjah, a poppy-growing southern area that had eluded government control for years.

A US commander based in Kandahar said that most combat operations had subsided, although US, British and Afghan troops would still need several weeks to exert control over more remote villages in the area of Helmand province.

"There will be some sporadic fighting, I believe, some tough areas where there are still a few holdouts," Brigadier General Ben Hodges told the PBS Newshour on US public television.

"I think most of the significant combat operations, though, will have subsided," Hodges said.

"I think the majority of the enemy has either been killed or driven out or blended back into the population," he said.

The assault has been billed as the biggest military operation since the 2001 US-led invasion ended the Taliban regime, and is a major test of US President Barack Obama's troop surge aimed at turning the tide in Afghanistan.

In a vivid reminder of the Taliban's reach, suicide bombers on Friday targeted guesthouses in the heart of the capital Kabul, killing 16 people including Westerners and Indians.

The new US-led counter-insurgency strategy, designed to allow Western troops to be drawn down by mid-2011, dictates military preparation and assault, then establishing civilian security and services such as hospitals and schools.

More than 4,000 families left Marjah amid the assault, many of them taking refuge in the provincial capital Lashkar Gah as food, medicine and other supplies ran low, humanitarian workers said.

But NATO said bazaars were opening and that rebuilding work had already begun on roads and bridges destroyed in the fighting. It warned, however, of the danger of hidden bombs.

In Washington, a senior Obama administration official said that Operation Mushtarak was just a preview of a wider campaign in the works to exert control in Kandahar, Afghanistan's second largest city.

"I think the way to look at Marjah, it's the tactical prelude to larger, more comprehensive operations later this year in Kandahar city," the official said on condition of anonymity.

"It's a goal for 2010. If our overall goal for 2010 is to reverse the momentum and gain time and space for the Afghan capacity, we have to get to Kandahar this year," he said.

Kandahar is a cultural home to the Pashtun people and was the birthplace of the Taliban movement, which imposed an austere brand of Islam over the country from 1996 to 2001.

"It's their center of gravity," the administration official said of Kandahar, describing the US goal as being able to bring "comprehensive population security" to the city.

Alexander Vershbow, the assistant secretary of defense for international security affairs, said that the Marjah offensive was "crucially important" for the Obama strategy.

"The goal of the new strategy is to reverse the Taliban's momentum, secure the population, and redouble efforts to build the Afghan national security forces so that they can take over security responsibility as conditions permit," he told reporters.

The anonymous administration official on Friday pointed to successes in a key part of the strategy -- Pakistan.

"In the last nine months we've seen a significant strategic shift in Pakistan," the official said. "That strategic shift is the decision by the Pakistani security forces to take the fight against the Pakistani Taliban."

Pakistan has launched offensives in its lawless tribal belt bordering Afghanistan, where much of the Taliban and Al-Qaeda leadership is believed to be based.

US officials have long suspected that elements in Pakistan's powerful spy agency have abetted extremists.