TOKYO (REUTERS) - A Japanese government panel warns there is "absolutely" no guarantee that domestic investors will keep buying government bonds, citing the risk of a spike in bond yields that could crimp long-term growth prospects, according to a draft report seen by Reuters on Monday.

The warning from the advisory panel to Finance Minister Taro Aso comes at a critical juncture. The government bond market has recently seen volatile price declines, underscoring a delicate balancing act for Prime Minister Shinzo Abe's government.

Mr Abe has unleashed massive fiscal and monetary stimulus to spur short-term growth, which has sent stock prices soaring.

But at the same time, he is trying to convince investors that over the longer term Japan will tackle a public debt that, at more than twice the nation's annual economic output, is the biggest in the developed world.