Afghan President Hamid Karzai says that U.S. plans to start withdrawing troops from his country next year has boosted the Taliban's spirits.

Speaking to a visiting U.S. congressional delegation in Kabul, Karzai said the July withdrawal date had provided "morale value" to the insurgency, the presidential office said.

Karzai also told the head of U.S. Central Command, Gen. James Mattis, that terrorism could not be defeated without rooting out terrorist sanctuaries across the border, a likely reference to Pakistan, where the Taliban and other groups are believed to recruit fighters and base their leadership.

The increasingly outspoken Afghan leader's comments echo a common complaint among U.S. President Barack Obama's critics that the deadline gives the Taliban motivation to hold out until after next July and then make a new push for power. Obama has stressed that any troop withdrawals will be linked to the security situation, and American military leaders have recently been saying it could take much longer to train Afghan forces.

Canada plans to end its combat role in Afghanistan beginning in the summer of 2011.

Violence has spiked around the country as the Taliban push back against a new security mission by the U.S.-led international force — bolstered by 30,000 U.S. troops in the insurgents' southern and eastern strongholds.

An insurgent attack killed eight Afghan police in the country's increasingly volatile north Thursday.

More than 10 militants attacked the police checkpoint outside the northern city of Kunduz, said provincial police chief Abdul Raziq Yaqoubi, adding it is suspected the attackers were jihadists from Russia's restive Chechnya region who are active in the surrounding province, also called Kunduz.

He said two or three of the militants were wounded when the police fought back. The militants apparently hoped to steal the policemen's weapons but were beaten back before they could do so, he said.

Kunduz has seen an increasing number of attacks on Afghan and foreign coalition forces that rely on a supply line running south through the province from neighbouring Tajikistan. Foreign fighters from Chechnya, Pakistan and the Persian Gulf infiltrate the region from the rugged mountainous border with Pakistan to the east.