In August Chinese investors sold off more US stocks and bonds than at any time in the last four years, according to new data released by the US Treasury Department on Thursday.

US equity sales in China added up to about $5.1 billion, a record for sales of US stocks by investors in China, while agency bond sales were also brisk.

According to the data, the holdings of US Treasuries by China dropped to $805.4 billion, falling to the lowest level seen since May 2009, when China held $776.4 billion of US debt.

Analysts speculated that the sell off of US equities and bonds was done to prop up the weakening national currency.

The yuan had fallen to its lowest exchange rate since November against the US dollar, leading Beijing to order increased interventions in the currency markets by state-owned banks.

Gennadiy Goldberg, head of US rates strategy at TD Securities in New York said, “It’s unclear whether this was for currency purposes because Chinese reserves have not declined, which is odd. It’s really difficult to tell why their holdings are declining so much, but it could certainly be to stabilize the currency.”

In August, the total holdings of US Treasuries by foreign countries amounted to $7.707 trillion, translating to a year over year growth rate of about 2.8%.

Japan is still the biggest foreign holder of US government debt at $1.11 trillion.