Taliban insurgents are increasingly using heavy weapons and more sophisticated roadside bombs. NATO forces are focusing efforts on targeting Taliban leaders to disrupt mutineers in eastern Afghanistan.
U.S. Brig. Gen. Joseph Votel, deputy commander of NATO troops in the volatile eastern region, said troops were going after both mid- and high-level leaders.
"We've removed a number of key leaders - insurgent leaders - off the battlefield here in regional command East, either killed or captured. That has disrupted them," he said in a video conference with reporters at NATO headquarters.
However, he said there were signs that new leaders were taking over, including well-trained foreigners.
"What the foreign fighters do is bring a little bit of leadership and bring some tactics and techniques that they may be imparting to some of the other insurgent groups here, which might allow them to operate a bit more effectively," he said from the NATO base at Bagram, Afghanistan.
Afghanistan's eastern region, where U.S. troops make up the bulk of the NATO force, has seen much of the resurgence in fighting this year, the most violent since American-led forces overthrew the Taliban regime after the 9/11 attacks in 2001.
Votel said the number of attacks with so-called improvised explosive devices was up 24 percent since the start of the year in the region. Suicide bombings are up by 17 percent.
"What we see in some cases is increased use of heavier weapons designed to potentially impact our aircraft or the some of the up-armored vehicles that we have," he said. "We continue to see use of improvised explosive devices, in some cases approaching greater levels of sophistication."
However, he said much of the upsurge in violence was due to more aggressive tactics by NATO's 41,000-strong International Security Assistance Force, which has sent more troops into the region to pursue the insurgents into their remote hideouts.
"We are in regions where ISAF forces have not been before, where the insurgents have had some free movement," he said. "Now we are in their support areas interdicting them, causing them to react. I think that accounts for a lot of what's been reported as an increase in violence."
Votel praised the Afghan army, saying it was becoming an increasingly reliable ally in the region, having recently taken the lead in two operations against the Taliban with NATO troops playing a support role.
"We see some very good Afghan leadership that is very, very capable of stepping up and taking responsibility," he said. "In most cases, they have really stood up to the task in hand."