News of an intensified search in Pakistan's tribal areas for the Al Qaeda leaders was first reported by ABC News and later confirmed by FOX News.
The U.S. official called the hunt for bin Laden a long-term process and denied that the trail had gone cold.
When "actionable" intelligence on the whereabouts of Usama bin Laden or his deputy is obtained, the U.S. moves resources accordingly, the official said.
The source would not reveal a specific area where the hunt was being conducted, but did not deny that the focus has been on North Waziristan, which lies along Pakistan's border with Afghanistan.
Last week, Director of National Intelligence Mike McConnell testified on the hill that current intelligence put both bin Laden and al Zawahiri in Pakistan.
Intelligence officials have said bin Laden has changed locations in the past during the month of March, traveling to hiding places in the mountains once the snow begins to melt.
FOX News' Catherine Herridge contributed to this report.