Bulk data storage allows for the "potential of abuse", President Obama has said, as he announced plans to curb the National Security Agency's authority.
"While few doubt the legitimacy of spying on hostile states, individuals acting on their own is a new threat," Mr Obama said.
"These signals intelligence efforts have prevented multiple attacks and saved innocent lives, not just in the United States but around the globe. But the risk of government overreach has also become more pronounced".
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Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.
The Westminster terror attack dominates the front pages of Thursday's newspapers.