BEIJING - China's central bank has pumped 870 billion yuan ($133.8 billion) into the market this week to ease a cash strain at a time when previous liquidity tools are maturing and companies are facing peak tax payments.

The People's Bank of China (PBOC) on Friday conducted 240 billion yuan of seven-day reverse repurchase agreements (repo), a process in which central banks buy securities from banks with an agreement to resell them in the future.

The operation followed a 250-billion-yuan reverse repo on Wednesday and one of 260 billion yuan on Thursday. With other liquidity tools maturing, the total net injection was 680 billion yuan this week.

That was just under a weekly record of 690 billion yuan seen in January and sharply up from a net injection of 70 billion yuan last week.

The reverse repo on Friday was priced to yield 2.25 percent, unchanged from Thursday, according to a PBOC statement.

The injection was taken as the central bank's earlier medium-term lending facility (MLF) operations, reaching billions of yuan, come to mature this month.

MLF is a tool 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.

In Friday's interbank market, the benchmark overnight Shanghai Interbank Offered Rate (Shibor), which measures the cost at which Chinese banks lend to one another, climbed by 0.9 basis point to 2.038 percent.