A Pentagon report said that the growth of Al-Qaeda safe havens in Pakistan's tribal areas is "troubling" and warned it may take Pakistan several years to turn around the situation.
The report to Congress by the US Department of Defence on Friday said Pakistan increased its troop levels in the border areas by 30,000 last year, and made "significant and costly" efforts to eliminate safe havens.
"It is troubling that despite these efforts, safe havens in the FATA have grown in recent years," the report said.
The report made no reference to an apparent change in strategy by the new Pakistani government favouring negotiations with militants in the federally administered tribal areas.
Under a peace agreement reached this week with pro-Taliban militants in the Swat Valley, the government agreed to gradually pull out its troops in return for a halt in attacks.
The Pentagon report noted that 700 Pakistanis have been killed in suicide attacks since July 2007. It said, "Al-Qaeda and other violent extremists continue to hide out in the FATA, where they are able to recruit, train, and target US and western interests, including plots against Europe and the US homeland."
Madrassas, or Islamic religious schools, "Continue to promote jihad and martyrdom, and provide potential operatives for acts of violence in Afghanistan," it said.
"Despite successful attacks against some terrorist training facilities in the tribal areas, it is believed other camps remain active and safe havens have grown in recent years," it said.
The report described a six-year US programme to help strengthen the Pakistani military and security forces' ability to secure the border with Pakistan, but cautioned that it will take time to implement.