Despite an casing of tensions with the United States, Pakistan is persistently undermining security in Afghanistan by permitting safe havens for insurgents, a Pentagon report said Monday.

In a twice-a-year war assessment mandated by Congress, the Defense Department said that the 68.000 US troops in Afghanistan and their allies had succeeded in preventing Taliban advances while limiting civilian casualties.

But Taliban havens across the border in Pakistan, the limited capacity of the Afghan government and 'endemic corruption' pose the greatest risks as the United States prepares to pull out troops by the end of 2014. the Pentagon said.

The report noted the better US relations with Pakistan, which agreed in July to reopen Western forces' supply routes into Afghanistan. Pakistan had refused access after a US border strike killed 24 of its troops in Novemher20l I.