The most vibrant market for yuan trading outside mainland China has turned into a key battleground for Beijing to defend the Chinese currency. Suspected intervention by Chinese banks in what’s known as Hong Kong’s “offshore” market has led to a surge in the cost for banks in the territory to borrow yuan from each other, The Wall Street Journal reports. Investors and analysts believe the intervention – which they say has likely come at the behest of China’s central bank – is aimed at thwarting bets against the Chinese currency, also known as the renminbi. On Monday, the overnight interbank yuan borrowing rate in Hong Kong reached 5.5155%, its highest since Feb. 19. The rate breached 5% on Thursday, ending a nearly two-month stretch of relative calm.