China set another firm fix for its currency on Tuesday and stepped up a verbal campaign, backed by what dealers said was aggressive buying, to convince sceptical investors that they were in control of events. Analysts said offshore buying by state-owned banks, under the direction of the People’s Bank of China (PBOC), dried up yuan liquidity to such an extent that overnight yuan borrowing rates in Hong Kong (HIBOR) hit a record 66.8 percent, and the spread between onshore and offshore yuan exchange rates briefly evaporated.