Taliban attacks up slightly this April-September vs 2011

NATO troops inspect the site of a suicide bomb attack in Kabul November 21, 2012.

WASHINGTON (Reuters) - Attacks by Taliban insurgents in Afghanistan rose slightly during the main part of the fighting season this year as U.S. surge forces withdrew and the transition to Afghan security lead picked up pace, according to a Pentagon report released on Monday.

Taliban-initiated attacks rose by 1 percent during the April-through-September reporting period compared to 2011, in part because a shortened poppy harvest freed low-level insurgents to begin the fighting season early, the semi-annual progress report to Congress said.

The rise came as Afghan security forces took on more and more responsibility for security in the country. About 76 percent of the population lived in areas where Afghan police and troops had the lead role in providing security, said the "Report on Progress toward Security and Stability in Afghanistan."

Several security issues remained challenging for international forces, especially the increasing number of attacks on foreign troops by members of the Afghan military, the report said.

"The rise in insider attacks has the potential to adversely affect the coalition's political landscape," the report said, adding that policies were being implemented to try to reduce the problem.

The report cited several other factors as undermining long-term stability in Afghanistan.

"The insurgency's safe havens in Pakistan, the limited institutional capacity of the Afghan government and endemic corruption remain the greatest risks to long-term stability and sustainable security in Afghanistan," the report said. (Reporting By David Alexander; Editing by Philip Barbara and Jackie Frank)