REUTERS, London

The dollar fell against most major currencies on Wednesday after the US signalled it may be nearing a deal with Iran, while the Japanese yen suddenly jumped to a more than two-month high as markets braced for ​another round of official buying from Tokyo.

The yen rose by as much as 1.8 percent earlier in a swift ‌move that left the dollar at a session low of 155, around its weakest since February 24. The dollar had earlier broadly strengthened against a range of currencies before a sudden move lower against the yen, which triggered speculation of another round of intervention.

Japanese Finance Minister Satsuki Katayama ​earlier in the week warned against speculative moves in foreign exchange, after a brief jolt higher in the yen sparked ​speculation Tokyo had again intervened to support the currency.

“As I have said repeatedly, we will take decisive measures against speculative moves, in accordance with the statement signed between Japan and the United States last year,” Katayama told ​reporters after the Asian Development Bank’s annual meeting in Uzbekistan. The Ministry of Finance of Japan could not be reached immediately for ​comment during a local holiday.

Part of the problem for Japanese authorities in staving off persistent weakness in the yen lies in markets that are beyond their immediate control, such as higher US Treasury yields, which favour the dollar, and oil, CIBC Capital Markets head of G10 FX strategy Jeremy ​Stretch said.

“It’s very tough to get the yen down if oil is going to remain elevated and/or US Treasury yields ​are, in terms of 10-years, you’re nearer 4.4 percent than you are 4.2 percent. So that was always going to be the difficulty the Japanese were ‌going to have.