KABUL: The head of Nato said Tuesday he was confident Pakistan's nuclear weapons were safe, but admitted it was a matter of concern, the day after the worst assault on a Pakistani military base in two years.

Anders Fogh Rasmussen was in Afghanistan on a one-day visit and met President Hamid Karzai to discuss the transition of security from Nato-led troops to Afghan security forces, which is due to begin in July.

Rasmussen was asked if Nato was concerned about Pakistan's nuclear weapons after it took Pakistani forces 17 hours to reclaim control of a naval air base from Taliban attackers and following the death of Osama bin Laden.

“I feel confident that Pakistan's nuclear arsenal is safe and well protected,” said Rasmussen. “But of course it is a matter of concern and we follow the situation closely.”

The attack in Karachi, the worst on a base since the army headquarters was besieged in October 2009, piled further embarrassment on Pakistan three weeks after the al Qaeda leader was found living in the city of Abbottabad, close to the country's military academy.

Rasmussen was scheduled to wind up his Afghan visit on Tuesday after spending a night and a full day in Afghanistan.