By Tetsushi Kajimoto and Izumi Nakagawa

TOKYO (Reuters) - Japanese manufacturers' mood soured in August to its lowest since 2013 when the central bank embarked on aggressive monetary easing, a Reuters poll showed, reflecting the pain caused by a rising yen and highlighting the huge task facing policymakers to generate growth.

The Reuters Tankan, which tracks the Bank of Japan's quarterly tankan survey, found the service sector's mood rose for the first time in five months, a sign of fragility rather than strength in private consumption that constitutes about 60 percent of the economy.

The monthly poll of 533 big and mid-sized firms on August 1-16, of which 275 responded, was taken just as Prime Minister Shinzo Abe unveiled new economic stimulus early this month, which appeared to have little impact on Japanese business morale.

The survey comes on the heels of data that showed the economy stalled in the second quarter as weak exports and a strong yen curbed capital expenditure.

With the yen near a seven-week high of around 100 to the dollar <JPY=>, exporters of cars and electronics complained about a profit squeeze, although a stronger currency also drives down the cost of imports.

"Domestic car sales have declined and we have suffered a foreign-exchange loss for exports due to appreciation of the yen," a manager at a transport equipment maker said in the survey, which companies answer anonymously.

"The yen's rise helps lower the cost of imports for raw materials, but we don't feel strength in demand for our products," said a textiles/paper producer.

The sentiment index for manufacturers fell to 1 from 3 in July, hurt by manufacturing industries including cars, food, machinery and electronics. It was seen bouncing to 6 in November.

The sentiment indexes subtract the percentage of companies saying conditions are poor from those saying conditions are good. A positive number means optimists outnumber pessimists.

The service-sector index rose to 18 from 15 in July, reflecting gains in retailers, real estate and other services.

The index was seen rising further to 19 in November.

Abe's cabinet this month unveiled stimulus of 13.5 trillion yen ($135 billion) in fiscal measures, hoping it would help the economy counter external headwinds and sustain a recovery.

The Bank of Japan expanded monetary stimulus last month via a modest increase in purchases of risky assets and it remains under pressure to do more in September, when it conducts a comprehensive review of the effects of its stimulus program.

(Reporting by Tetsushi Kajimoto; Editing by Eric Meijer)