The top U.S. intelligence official says he could never agree with a decision to pardon Edward Snowden.

Snowden was an National Security Agency contract employee when he took more than a million documents and leaked them to journalists who revealed massive domestic surveillance programs begun in the aftermath of the 9/11 attacks. The programs collected the telephone metadata records of millions of Americans and examined emails from overseas.

Human rights groups are seeking a presidential pardon for Snowden.

National Intelligence Director James Clapper said Tuesday that he might understand a pardon if what Snowden exposed was limited to domestic surveillance.

But Clapper said at an event hosted by The Washington Post that Snowden damaged U.S. capability to battle foreign threats and erased U.S. capabilities used to protect troops in Afghanistan.