Bill Gross, the manager of the world's largest bond fund, raised his bet against U.S. government-related debt in April to 4 percent from 3 percent, according to PIMCO's website on Monday.

The increase, albeit small, follows Gross' move to ratchet up his bearishness in March by taking his initial short position in U.S. government-related debt, which includes Treasuries, TIPS, agencies, interest rate swaps, Treasury futures and options and FDIC-guaranteed corporate securities.

The $240 billion Total Return fund also raised its cash position to 37 percent in April from 31 percent in March, the website added.

(Editing by Andrew Hay)