Pakistan has closed its borders to NATO supplies, and gave the U.S. 15 days to vacate an air base used for drone strikes, after a NATO attack reportedly killed 24 Pakistani soldiers on Saturday, the Financial Times reports. U.S. officials profusely apologized for the accident, which they said was “highly likely” caused by a NATO aircraft. But the deaths of Pakistani troops, who may have been mistaken for Taliban militants along the ill-marked border, threw a new wedge between Washington and Islamabad at a time when the U.S. needs Pakistan’s cooperation to ensure an orderly withdraw from Afghanistan and to pressure the Taliban into negotiations. The diplomatic rift also gave China an opportunity to play up its strategic posturing as Pakistan’s ally, Reuters reports. “China believes that Pakistan’s independence, sovereignty and territorial integrity should be respected and the incident should be thoroughly investigated and be handled properly,” a Foreign Ministry spokesman said in a statement.