Chinese military spending exceeded $145 billion last year as it advanced a program modernizing an arsenal of drones, warships, jets, missiles and cyber weapons, the Pentagon said on Thursday, offering a far higher figure than Beijing's official tally.

The Pentagon's estimate, using 2013 prices and exchange rates, was 21 percent above the $119.5 billion figure announced by China. It was detailed in an annual report to Congress that cited steady progress in Chinese defense capabilities.

It acknowledged that estimating Chinese spending can be difficult, in part because of "poor accounting transparency and incomplete transition from a command economy."

Admiral Samuel Locklear, head of the US Pacific Command, told US lawmakers in March that a strong China had the potential to advance global security.

"The question is: 'Is (China's military) spending transparent? What is it used for?'" he asked.

Japan's chief cabinet secretary, Yoshihide Suga, said China's lack of clarity in its defence policy and spending was a global concern.