Washington, May 2 (IANS): US-led coalition forces have weakened the Taliban in Afghanistan, but terrorist safe havens in Pakistan and endemic corruption still pose tough challenges, a new Pentagon report says.

"The Taliban-led insurgency's safe haven in Pakistan, as well as the limited capacity of the Afghan Government, remain the biggest risks to the process of turning security gains into a durable and sustainable Afghanistan," the latest semi-annual Pentagon report to the Congress Tuesday said.

Insurgents "still operate with impunity from sanctuaries in Pakistan," the report said. For example, insurgents slip across the border from Pakistan into Logar and Wardak provinces in the east, and from there stage attacks on Kabul.

"Challenges remain," a senior defence official told reporters in a background briefing on the report. "The most important of those challenges, of course, remains the sanctuaries in Pakistan and the ability of the Taliban to refit, regroup and rearm there."

The Taliban and the Haqqani network use areas in Pakistan's federally administered tribal areas to attack Afghan and NATO troops. Afghan and NATO leaders continue to urge Pakistan to address this problem.

"It's Pakistan's duty as a responsible international country to control all violence that emanates from its borders into other areas," the official said. "And we continue to urge them to do so."

NATO's campaign plan is designed to work at reducing the ability of the Taliban and the Haqqani network to infiltrate over the border launch attacks in Afghanistan.

"It's not perfect, so we're going to have to continue to work to shield Afghanistan and work to build the capacity of the Afghans to shield them from these things, from these attacks, but I think we will continue the efforts as well with Pakistan," he said.