FACTBOX: Pakistan's nuclear arsenal

(Reuters) - Some security experts fear Pakistan's nuclear weapons could be compromised or fall into the hands of Islamic militants as the country's instability deepens in the wake of Benazir Bhutto's assassination.

Here some details about Pakistan's nuclear capability:

* NUCLEAR SAFETY - WHAT COULD HAPPEN?

-- Pentagon officials say Pakistan's nuclear arsenal is secure in military hands, but some U.S. lawmakers and experts warn that nuclear material and designs could leak out if political instability persists.

-- Musharraf has concentrated control over Pakistan's nuclear weapons but a decline in his support within the military amid the current political crisis could raise a risk that control over the weapons could weaken.

-- That could open the door to theft or sale of weapons material to extremist groups, some experts say.

-- The military is suspected by some of at least knowing about the smuggling activities of Pakistan's A.Q. Khan network, which sold weapons technology to Iran, North Korea and Libya.

* WHAT IS KNOWN ABOUT PAKISTAN'S ARSENAL?

-- Pakistan embarked on a nuclear weapon program in the early 1970s after its defeat and break up in the 1971 Indo-Bangladesh war. Islamabad regards nuclear weapons as essential to safeguard the South Asian balance of power and offset its conventional inferiority and lack of strategic depth against India.