[TOKYO] Japan's top currency diplomat said on Thursday that Japanese financial authorities are watching for speculative currency market moves and would respond if needed.
Masatsugu Asakawa, vice finance minister for international affairs, said "We are worried that there are nervous moves in the currency market".
"If speculative moves continue to be seen, we are ready to take necessary action," he said.
He added that authorities will monitor the currency market in the evening even more carefully than usual.
Mr Asakawa spoke following a meeting, held on a public holiday, that involved the finance ministry, Financial Services Agency and the Bank of Japan (BOJ).
At the meeting, there was discussion of policy decisions in the past day from central banks in Japan and the United States.
Such meetings are not routinely scheduled, but neither are they considered unusual.
On Thursday, following the Fed decision to keep policy steady, the dollar tumbled to a near four-week low of 100.1 against the yen, before paring losses.
On Wednesday, the BOJ added a long-term interest rate target to its massive asset-buying programme, overhauling its policy framework and recommitting to reaching its two per cent inflation target as quickly as possible.
Most Japanese corporate profits will take a hit by the stronger yen as their overseas profits could be eroded when repatriated.