By Susan Cornwell
WASHINGTON (Reuters) - Even as the United States begins to withdraw from Afghanistan, insurgents abetted by Pakistan pose the major threat to U.S.-led forces, the Pentagon said on Friday.
Security has improved in recent months and enemy attacks are down in Afghanistan compared to a year ago, the Pentagon said in a twice-annual report to the U.S. Congress.
NATO and Afghan forces largely "stunted" the Taliban's spring and summer offensive, although the insurgency remains adaptive and resilient, with a "significant regenerative capacity," the report said.
But attacks from across the eastern border were up because of the support the insurgency received from safe havens in Pakistan, it said.
"Safe havens in Pakistan remain the insurgency's greatest enabler," the report said. These havens have grown more "virulent" in recent months "and are the most significant risk" to NATO's campaign, it said.
The report comes as President Barack Obama's administration has begun pulling surge forces from Afghanistan -- withdrawing 10,000 this year and the remaining 23,000 by the end of September 2012.
Critics of Obama's plan fear it could undermine the progress surge troops have made and point to faltering security in attacks in Afghanistan's volatile east, along the porous border with Pakistan.
The Afghanistan NGO Safety Office (ANSO), which advises aid and other groups on security, warned this month that the war appeared to be "escalating, not diminishing."
The Pentagon said that recent high-profile attacks in Kabul, including a bold September 13 strike on the U.S. Embassy that rattled perceptions about security in the capital, were carried out by the Pakistan-based Haqqani network and "directly enabled by Pakistan safe haven and support."
While high-profile attacks on "soft targets" have increased, overall enemy attacks were five percent lower than the same period a year earlier, said the report, which covers April 1 through September 30. It said enemy attacks continue to decline.
Assassinations and attacks directed from the safe havens in Pakistan could have a "significant political effect" in Afghanistan as well as coalition countries, the document said. Afghan perceptions of security had worsened slightly, it said.
Civilian casualties remained elevated, although the Pentagon noted that most of them were caused by insurgents or roadside bombs, rather than NATO operations.
The report said the security gains provide a firm foundation for gradually putting Afghan forces in charge of security, a goal now set for the end of 2014.
Yet serious doubts remain about how quickly the improving but inexperienced Afghan army and police can take over -- and how long Washington will be willing to pay for them.
Lasting stability was also threatened by a weak Afghan government, it said. Widespread corruption, political disputes and lack of progress toward reforms were threatening the government's long-term viability. The influence of criminal patronage networks on the Afghan military also posed a threat.
It said the death of al Qaeda leader Osama bin Laden at the hands of U.S. forces in Pakistan was an important achievement, but strained U.S.-Pakistani ties. U.S. officials have said that communications between foreign forces in Afghanistan and Pakistani soldiers have been inadequate.
Mistrust and divergent interests will also continue to make cooperation difficult between Afghan and Pakistani officials, it said.
Iran also continues to provide lethal aid to insurgents, including weapons and training, the report said.
For the rest of this year, the Pentagon expects that the Taliban-led insurgency's main effort will focus on regaining control of safe havens and population centers in Helmand and Kandahar provinces.
Kabul would remain a target for high-profile attacks and assassination attempts.
The Haqqani network's main effort will be to re-exert dominance in Khost, Paktika and Paktia provinces, and "it will also continue to target Kabul with high-profile attacks in an effort to maintain its influence on the reconciliation process."
(Reporting by Susan Cornwell; Editing by Anthony Boadle)