WASHINGTON (Reuters) - A high-ranking al Qaeda leader sought by the United States in its war on terrorism was captured recently and is in American custody, U.S. government sources said. The sources declined Friday to name the operative for Osama bin Laden's network, caught in the past week or so, but said he was in the top dozen and ranked him similar to Abu Zubaydah who is one of the most senior members of al Qaeda in U.S. custody.

The captured al Qaeda leader was not as high-ranking as those in bin Laden's most inner circle, such as top lieutenant Ayman al-Zawahri and operational leader Khalid Shaikh Mohammed, who have not been found. He also was not bin Laden's son Saad, sought by U.S. authorities who say he is active in al Qaeda, they said.

The United States has vowed to destroy bin Laden and his al Qaeda network in retaliation for the Sept. 11, 2001, attacks on America that killed about 3,000 people. Roughly half of the top two-dozen al Qaeda leaders have either been killed or captured since the United States started hunting them down after the Sept. 11 hijacked-plane attacks. Earlier this month an unmanned CIA drone fired a missile at a car in Yemen and killed six suspected al Qaeda members. Qaeda leaders Zubaydah and Ramzi Binalshibh were caught in separate operations in Pakistan earlier this year. They are being interrogated at an undisclosed location.

Zubaydah was a top bin Laden deputy who officials say recruited al Qaeda members and coordinated their travels in and out of Afghan training camps. U.S. officials have said he has provided important information during interrogations.

PRIZE CATCH

The recently captured al Qaeda leader, who has not been identified, is considered a prize catch for U.S. authorities similar to Zubaydah. But bin Laden has still not been found and apparently survived the U.S.-led bombing on Afghanistan. U.S. officials believe an audiotape broadcast earlier this week on the Qatar-based al-Jazeera television channel is bin Laden praising recent attacks and making fresh threats. The U.S. military and intelligence agencies have scoured areas near the border of Afghanistan and Pakistan for signs of bin Laden and his followers.

"There have been a number of -- numerous senior leaders of al Qaeda that have either been eliminated, incarcerated or detained someplace," U.S. national security adviser Condoleezza Rice said without elaborating. U.S. authorities have been concerned this week that al Qaeda was planning new violence. The FBI said the network may favor "spectacular attacks" that result in mass casualties and severe damage to the U.S. economy. The audiotape contributed to that concern. Past bin Laden tapes have sometimes been followed by attacks. Authorities have also noted an increased level of "chatter," or communications between al Qaeda operatives picked up by intelligence agencies, as in the months before Sept. 11, 2001.