At the same time, he asserted that the US would still prefer to detain and prosecute terrorists and would resort to lethal actions only to save lives of people.
"Despite our first preference for detention and prosecution of terrorists - that's our first preference - sometimes, lethal action is necessary in order to protect US lives, and we are convinced of the legality as well as the soundness of the basis for making that determination," Kerry said in defense of his country's drone policy.
"Clearly our actions are effective because dozens of highly trained, skilled al-Qaida commanders, trainers, bomb makers and operatives have been taken off the battlefield," Kerry said in a joint news conference with his German counterpart Guido Westerwelle.
"The fact is that plots have been disrupted before they were able to be carried out, and they would have targeted international aviation, US transit systems, European cities and our troops in Afghanistan, and those strikes have saved lives," he argued in response to a question.
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Kerry said he has personally reviewed the policy.
"When I first came in here, I reviewed this policy personally because I was concerned as a Secretary of State about the conditions by which it is conducted," he said.