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KABUL - On the surface, it would seem unlikely that Afghan President Hamid Karzai, who presides over a politically feeble government and is highly dependent on the United States military presence and economic assistance, would defy the United States on the issue of peace negotiations with the leadership of the Taliban insurgency.

But a long-simmering conflict between Karzai and key officials of the Barack Obama administration over that issue came to a head at last week's London conference, when the Afghan president refused to heed US signals to back off his proposal to invite the Taliban leaders to participate in a nationwide peace...