Japan kept up its warnings over speculative currency moves following the yen’s slump to a three-decade low, as it tried to dissuade traders from testing its intervention strategy.

The currency fell to its lowest since August 1990 in the aftermath of Thursday’s hotter-than-expected U.S. inflation report, before a rapid reversal that raised market chatter of potential action by Japanese authorities.

"We can’t tolerate excessive moves triggered by speculation,” said Finance Minister Shunichi Suzuki in Washington, where he attended Group of 20 meetings. "We’re watching the foreign exchange markets with a high sense of urgency, and we’ll take appropriate responses against excessive moves.”