NATO-led troops have resumed most joint operations with Afghan forces after commanders restricted patrols with their allies in Afghanistan due to a spike in insider attacks, US Defense Secretary Leon Panetta said Thursday.

Last week, the International Security Assistance Force announced a scaling back of joint operations with its Afghan partners following a dramatic rise in so-called "green-on-blue" assaults, in which Afghan soldiers turn their weapons on their Western allies.

"I can now report to you that most ISAF units have returned to their normal partnered options at all levels," Panetta told a news conference.

But the Pentagon chief, who was joined by top US military officer General Martin Dempsey, could not provide details as to what percentage of joint operations had resumed.

Although the defense chiefs insisted the partnership was effectively back to normal, US military officers acknowledged that a new approval process that required two-star generals to endorse any joint patrols below the battalion level was still in place.

ISAF, responding to a mounting threat from insider assaults, had said on September 18 that joint patrols and other operations with Afghan troops would be carried out only at the battalion level and above, while activities with smaller units would have to be approved by two-star regional commanders.

The order has not been rescinded and the ISAF Joint Command "directive remains in effect," said Dempsey's spokesman, Colonel Dave Lapan. "Assessments continue."

Dempsey, chairman of the US Joint Chiefs of Staff, said he conferred with coalition commanders this week in an unannounced visit to Afghanistan and that joint operations had been restored for the most part.

"When I left Afghanistan, the leaders I had spoken to had resumed operations as they had been previously organized," Dempsey said.

Panetta vowed that the insider threat would not derail plans to transfer security to Afghan forces by the end of 2014, paving the way for the withdrawal of most NATO combat forces.

"We must and we will take whatever steps are necessary to protect our forces. But I also want to underscore that we remain fully committed to our strategy of transitioning to Afghan security control," he said.

The insider attacks pose a potential serious threat to the NATO war effort, which has portrayed the advising and training of Afghan forces as the key to the scheduled pullout of Western troops.

According to the Pentagon, 51 ISAF troops have been killed in 35 insider incidents this year, accounting for about 20 percent of all coalition casualties in the war.

Despite the rise in insider attacks, Panetta said the war against the Taliban was making headway and credited a US troop surge with turning the tide.

President Barack Obama ordered in 33,000 reinforcements in December 2009 and the last of the "surge" troops pulled out of Afghanistan last week, leaving 68,000 US boots on the ground -- part of a NATO-led force of roughly 112,000.

Arguing the surge was a success, Panetta said beforehand that "there was a real risk that the mission in Afghanistan might very well fail" and that the Taliban would take back power.

But he said the insurgency had been weakened and Afghan government forces strengthened.

"The Taliban's gains on the battlefield have been reversed. They've been unable to regain any of the territory that they've lost," he said.

The effect of the troop surge remains the subject of debate, with US officials saying the Taliban was rolled back in its spiritual heartland in the south.

The Pentagon cited figures showing insurgent attacks on NATO-led forces this year had decreased about five percent compared to 2011.

But the level of violence still exceeded that from the summer of 2009, before Obama opted to deploy additional troops, according to ISAF's website.

While the number of recorded attacks on ISAF troops are down from 2011, the statistics do not appear to take into account the expanded combat role of Afghan government forces, who have been dying at five times the rate of NATO troops.

Critics have accused NATO and the United States of painting an overly optimistic picture of the conflict and warned that Afghan security forces could disintegrate, with the country reverting to civil war once the coalition combat troops depart by 2015.

At the outset of the surge, senior commanders had suggested that the influx of US forces would drive the Taliban to peace negotiations, but so far overtures designed to encourage talks have produced no major progress.