Adds background and details on last week suspected intervention

SINGAPORE, May 6 (Reuters) - The Japanese yen surged suddenly on Wednesday, with suspected intervention last week leading to a jump in the battered currency and traders on watch for further moves from Tokyo authorities.

The yen JPY=EBS was last at 156.15 per U.S. dollar, up 1% on the day. Trading was thinned with markets in Japan closed for a holiday. Japan's Ministry of Finance (MOF) was not immediately available for comment when contacted by Reuters.

Investors were wary of further intervention from Japanese authorities after sources told Reuters last week that Tokyo had stepped in to stem the yen's decline on Thursday. Data on Friday showed Tokyo may have spent as much as $35 billion to support the yen.

Japanese Finance Minister Satsuki Katayama on Monday warned against speculative moves in foreign exchange, after a brief jolt higher in the yen at the start of the week 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.

Traders at agent banks have been standing by to get intervention orders throughout the holiday period, a market source told Reuters.