U.S. Defense Secretary Leon Panetta says he believes the strategic defeat of al-Qaida is “within reach” after the killing of Osama bin Laden.

While on his first trip to Afghanistan since taking over at the Pentagon July 1, Panetta said the information gained during the U.S. raid that killed bin Laden in Pakistan, plus other intelligence Washington has collected over years, has resulted in an “active pursuit” of between 10 and 20 terrorist leaders in Pakistan, Yemen, Somalia and North Africa.

The defense secretary singled out al-Qaida's new leader Ayman al-Zawahri, saying the United States believes he is hiding in Pakistan's semi-autonomous tribal areas bordering Afghanistan. Panetta also mentioned Anwar al-Awlaki, a U.S.-born radical Muslim cleric believed to be living in Yemen.

While in Afghanistan, Panetta is scheduled to meet the top U.S. and NATO commander General David Petraeus and U.S. Ambassador Karl Eikenberry. He also plans to meet with Afghan President Hamid Karzai. The two men are familiar with each other from the years Panetta headed the CIA.

Panetta's recent transition from CIA chief to defense secretary comes at a time of strained relations between the two countries. In June, President Karzai used his final press conference alongside outgoing Defense Secretary Robert Gates to again voice his strong complaints on civilian casualties reportedly caused during coalition airstrikes.

Panetta also will oversee the start of U.S. President Barack Obama's planned pullout of 10,000 American troops during this year and another 23,000 by the middle of next year.

The pullout comes as critics debate whether Afghanistan is ready to take over its security responsibilities. There have been several major attacks in the capital, Kabul, this year, which is under the supervision of Afghan security forces and at the center of their influence.

Also, there have been several high-profile incidents of Afghan security force members turning on their coalition counterparts recently.

The latest occurred Saturday when Afghan police said a local guard shot and killed two coalition troops and wounded a third in the northern part of the country. The most recent incident before that happened in May when an Afghan soldier killed an Australian service member.