The yen jumped suddenly against the dollar on Thursday, with traders alert to the prospect of intervention from Japan to prop up its stubbornly weak currency.

It was not immediately clear what drove the market move or whether Japanese authorities were in the market. It appeared smaller than that after previous bouts of intervention.

Markets have been on alert for yen-buying by Japanese authorities, who have been warning of action for months as currency weakness exacerbates the cost-of-living impact of rocketing energy import prices.

MARKET REACTION:

FOREX: The dollar dropped as much as 0.9% to 161.115 yen FX_IDC:USDJPY and was last trading at 161.7, down 0.53%.

The yen also jumped against the euro, sterling and Australian dollar FX:EURJPY, FX:GBPJPY, FX:AUDJPY. It was last at 184.3 per euro and 215.2 per pound.

HIROFUMI SUZUKI, CHIEF FX STRATEGIST, SMBC, TOKYO:

"It is not clear whether it was intervention. However, as has been reported, it is possible that the authorities have shifted their intervention strategy and tactics, and may no longer be signaling the possibility of intervention in advance.

If anything, market participants may become increasingly suspicious, which could make it more difficult for the yen to weaken further."

BART WAKABAYASHI, BRANCH MANAGER, STATE STREET, TOKYO:

"The initial move looked like somebody was in the market, but the current way it is trading higher, we'd question it and I'd lean towards the rate-check rumour. The question is where this came from and it would be impactful if it were not the BOJ.

The market is nervous, and that move just proved that the market is nervous, which is good news for the Ministry of Finance."

TAKESHI ISHIDA, STRATEGIST AT KANSAI MIRAI BANK, OSAKA, JAPAN:

"If this (the decline in dollar-yen) was caused by the intervention, the move was small. The Japanese government might have stepped in the market in case the U.S. jobs data is strong. I was thinking the government would step in when the yen falls to 163-164 level.

The intervention would work better when the U.S. jobs data is weak as it will be hard for the Fed to justify the rate hike."

DEREK HALPENNY, HEAD OF RESEARCH GLOBAL MARKETS EMEA, MUFG, LONDON:

"I think it (dollar/yen move) is jittery price action. We have payrolls and a holiday, liquidity conditions will be thin, so markets are nervous about potential intervention."

ABBAS KESHVANI, ASIA MACRO STRATEGIST, RBC CAPITAL MARKETS, SINGAPORE:

"We will have to wait for data to ascertain if this was intervention, but the timing of the move does suggest that it was.

We can get more (intervention). They have communicated that they wish to be more nimble in their intervention, rather than defend a specific line in the sand. So their new approach allows them to intervene more frequently."

MOH SIONG SIM, STRATEGIST, OCBC, SINGAPORE:

"It is hard to tell. The move is too small for intervention. Possibly a rate check or some brave soul taking advantage of thinning liquidity into a long U.S. weekend."