Bloomberg reports that the Swiss National Bank appears to have stepped up its interventions to prevent the franc from strengthening last week, as haven assets around the world got a fillip from rising risk aversion.

The amount of cash commercial banks hold at the central bank, known as sight deposits, rose by 2.1 billion francs last week, the largest increase since early January, data on Monday showed.

Along with negative interest rates, interventions are part of the SNB's toolkit to prevent an undue strengthening of the franc. Swiss officials rarely say when they've been in the market, and so analysts closely scrutinize the sight deposit data for clues.

"It looks like the SNB intervened," said Credit Suisse economist Maxime Botteron. Still, activity appears to have been lower than in August, when the central bank was last suspected of launching a barrage of interventions to prevent the franc from strengthening, he said.

While markets in risk-off mode, "we've got to prepare for more interventions," Botteron also said.