The CIA has ended the use of vaccine programmes in its spying operations amid concerns for the safety of health workers, the White House has said.
In a letter to US public health schools, a White House aide said the CIA stopped such practices in August.
The CIA used a fake vaccine programme to try to find Osama Bin Laden before US special forces killed him in 2011.
The CIA's move comes after a wave of deadly attacks by militants on polio vaccination workers in Pakistan.
"By publicising this policy, our objective is to dispel one canard that militant groups have used as justification for cowardly attacks against vaccination providers," CIA spokesman Dean Boyd said in a statement to the BBC.
Sixty-six cases of polio have been declared in Pakistan since January, compared with only eight during the same period last year.
And more than 60 polio workers and security personnel were killed between December 2012 and April 2014, most of them in the Khyber Pakhtunkhwa province, according to Pakistani officials and humanitarian workers.
The geographical spread of the cases suggests they are mostly sourced to the north-western Waziristan tribal region, the BBC's Ilyas Khan reports from Islamabad. Militants controlling the region banned vaccination there, saying health workers may include American spies.
"This reassurance is coming at the right time and we sincerely hope this will contribute towards reaching the children," Zubair Mufti of the World Health Organization told the BBC. "Public health programmes should only be focused toward providing health to the people and not collateral things."
In a letter dated 16 May, the White House assistant to the president for homeland security and counter-terrorism, Lisa Monaco, wrote that CIA director John Brennan had directed the agency to cease "operational use of vaccine programmes".
Written By: BBC News
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