BEIJING - China's central bank said Thursday it had injected 525.8 billion yuan ($77.3 billion) into the market via MLF, SLF and PSL tools in May to maintain liquidity.

The People's Bank of China (PBOC) said it pumped 459 billion yuan via the medium-term lending facility (MLF) last month to keep interbank liquidity stable.

The PBOC offered 392.5 billion yuan of MLF loans that will mature in one year at an interest rate of 3.2 percent, and 66.5 billion yuan six-month MLF loans at 3.05 percent.

It brought the total outstanding MLF loans to 4.16 trillion yuan at the end of May.

The MLF tool was first introduced in 2014 to help commercial and policy banks maintain liquidity by allowing them to borrow from the central bank by using securities as collateral.

The central bank has increasingly relied on open-market operations for liquidity, rather than cuts in interest rates or reserve requirement ratios to maintain a prudent and neutral monetary policy.

In May, the PBOC also granted 19.2 billion yuan to financial institutions through the standing lending facility (SLF) to meet provisional liquidity demand.

In the same period, the central bank injected 47.6 billion yuan of funds through the pledged supplementary lending(PSL) to the China Development Bank, Agricultural Bank of China and the Export-Import Bank of China.