CIA Director Leon Panetta began the second day of his unannounced visit to Pakistan on Saturday.

Panetta, nominated to take over as defense secretary next month, held talks Friday with Pakistani Army Chief General Ashfaq Parvez Kayani and Pakistani spy chief Lieutenant General Ahmed Shuja Pasha.

Panetta's trip to Pakistan is his first since the secret May 2 raid by U.S. commandos that killed terror mastermind Osama bin Laden. Relations between the two countries have been strained since the raid.

On Thursday, Panetta told lawmakers in Washington that the U.S. must do everything it can to strengthen the “complicated” relationship with Pakistan.

He said it is clear that the U.S. cannot succeed in Afghanistan if it is not succeeding in neighboring Pakistan, controlling terrorist safe havens and cross-border attacks.

Pakistan received $2.7 billion in security-related assistance from the United States in the fiscal year that ended last October. Islamabad is the third-largest recipient of U.S. security aid and reimbursements, after Afghanistan and Israel.

Meanwhile, most of the U.S. experts sent to help train Pakistan's military in counterinsurgency have left the country at Islamabad's request.

Pakistan asked for the drawdown last month after U.S. commandos were able to infiltrate Pakistan to kill al-Qaida leader bin Laden.

Pakistani leaders said the action was a violation of its sovereignty.