The Bank of Japan (BOJ) has conducted an operation that is said to be an apparent preparation for currency intervention, local media reported on Wednesday, as policymakers stepped up warnings about sharp falls in the yen.

The financial daily Nikkei and other local media said the BOJ carried out a "rate check." The yen rose slightly from a near 24-year low against the dollar after the reports, which cited unidentified sources, and was trading around 143.89 at 5:20 a.m. GMT.

The currency has depreciated around 20% so far this year, as the BOJ has kept policy super-loose while many of its global peers, such as the U.S. Federal Reserve (Fed), have aggressively raised interest rates to combat surging inflation, making Japanese assets less attractive to investors.

Aside from verbal warnings, Japanese policymakers have several options to stem excessive yen falls. Among them is to directly intervene in the currency market, selling dollars and buying up large amounts of yen.

A rate check by the BOJ, a practice in which central bank officials call up dealers and ask for the price of buying or selling yen, is seen in currency markets as a possible precursor to action. When the BOJ made its check, the rate was around 144.9 to the dollar, Jiji news agency said, citing a market source. Nikkei’s report appeared on its website.

A rate check involves asking market participants about their foreign exchange trading.

"Basically it’s a warning, which is the next best thing to an intervention when the exchange rate is fluctuating," Toshikazu Horiuchi of IwaiCosmo Securities told Agence France-Presse (AFP)

"My feeling is that the Ministry of Finance won’t intervene at this stage and will leave it at verbal warnings," Takeshi Minami, chief economist at Norinchukin Research Institute in Tokyo told Reuters. "There’s still a week before the Fed’s rate-setting meeting. I don’t think markets believe the ministry will intervene at current dollar/yen levels."

Japanese Finance Minister Shunichi Suzuki said earlier on Wednesday that currency intervention was among the options the government would consider.

Masato Kanda, vice finance minister for international affairs, told reporters on Wednesday that the yen’s move was "rapid" and "concerning."

Data issued on Tuesday showing unexpectedly strong U.S. inflation for August prompted bets on the Fed raising interest rates higher and for longer, increasing downward pressure on the yen.

"Recent moves are rapid and one-sided, and we’re very concerned. If such moves continue, we must respond without ruling out any options," Suzuki told reporters on Wednesday.

"We’re talking about taking all available options, so it’s correct to think so," Suzuki said when asked whether yen-buying currency intervention was among the government’s options.

The remark was the strongest to date by government officials in signaling the possibility of currency intervention, which markets have nonetheless considered highly unlikely due to the difficulty Tokyo would face in getting agreement from its G-7 partners.

Once welcomed for giving exports a boost, the yen’s weakness is becoming a cause of headaches for Japanese policymakers because it hurts households and retailers by inflating the already rising prices of imported fuel and food.

The yen-buying intervention has been very rare. The last time Japan intervened to support its currency was in 1998 when the Asian financial crisis triggered a yen sell-off and a rapid capital outflow from the region. Before that, Tokyo intervened to counter yen falls in 1991-1992.

"When a rate check is conducted, sometimes it evolves into an intervention, so that’s why the market reacts very sensitively," Horiuchi said.

"But its actual impact hinges on whether an intervention is really possible."