"Reports that the trail has gone stone cold are not correct," said one U.S. official. "We are very much increasing our efforts there," the official said.
People familiar with the CIA operation say undercover officers with paramilitary training have been ordered into Pakistan and the area across the border with Afghanistan as part of the ramp-up.
THE BLOTTER RECOMMENDS
Although never publicly acknowledged, Pakistan has permitted CIA teams to secretly operate inside Pakistan.
Pakistan officials say they are aware that CIA teams have increased their presence in northern Waziristan since last September when Pakistan withdrew its troops from the area under a much-criticized "peace deal" with tribal leaders.
Director of National Intelligence Mike McConnell testified last week that current intelligence "to the best of our knowledge" puts both bin Laden and al Zawahri in Pakistan. It was the first time a high-ranking U.S. official publicly identified Pakistan as bin Laden's hiding place.
Past intelligence has indicated that bin Laden often changed locations in March, traveling to hiding places in the mountains once the snow cover begins to melt.