The U.S. role in civilian deaths has been a major sticking point in negotiations. Responding to massive public anger over the perceived indifference of the U.S. military to civilian deaths, Karzai wants greater Afghan control over "night raids." That's a catchall term for the military practice of entering and searching Afghan homes at night, in pursuit of militants and their supplies.
Kate Clark, of the Kabul-based Afghan Analysts Network, said the latest shootings are straining already tense relations.
"Relations are really irritable between the Americans and the Afghan government at the moment," Clark said. "This issue is just like a further irritant, like grit."
Associated Press writers Heidi Vogt in Kabul, Lolita C. Baldor traveling with Panetta and Matthew Lee, Robert Burns, Julie Pace and Kimberly Dozier in Washington contributed to this report.
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