Kabul, Afghanistan (CNN) -- U.S. Defense Secretary Leon Panetta warned Thursday that the United States was "reaching the limits of our patience" with Pakistan over militants that attack U.S. forces in neighboring Afghanistan from havens within its borders. "It's extremely important that Pakistan take action to prevent this kind of safe haven," he said during an unannounced visit to Kabul, and that militants cannot use the country as a "safety net" from which to attack U.S. soldiers. Afghan leader condemns NATO airstrike; U.S. defense secretary visits Kabul "We have made that very, very clear time and time again, and we will continue to do that," he said.
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NEW: Pakistani military official says U.S. comments are a way to pile pressure on Pakistan
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Pakistan's Washington envoy says Panetta's remarks are unhelpful
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U.S. defense secretary: Militants must not be able to use Pakistan as a "safety net"
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Panetta's criticism of Pakistan is not a significant change in tone, an analyst says
"This kind of public messaging from a senior member of the U.S. administration is taken very seriously in @placeholder and reduces the space for narrowing our bilateral differences at a critical time in the negotiations," she said.