tokyo feb 9 reuters  a future bank of japan boj interest rate hike could affect the countrys sovereign debt rating if firms struggle to absorb rising funding costs an official at sp global ratings said on thursday higher borrowing costs could also lead to a downturn in longterm economic growth sp said japanese bond yields have crept up on market expectations the boj will phase out its yield control policy and start raising interest rates under a new governor who succeeds incumbent haruhiko kuroda in april while further rises in longterm interest rates could increase japans already large debt burden such factors are already taken into account in the current a sovereign debt rating said kim eng tan senior director of sps sovereign ratings team in asiapacific the bigger concern is whether japanese firms accustomed to many years of ultralow interest rates could absorb higher funding costs that come from tighter monetary policy he told reuters in an interview sp expects the boj to tighten policy only gradually with the nearterm impact on the economy likely limited tan added but the longerterm effect on japanese firms and the broader economy is a concern as were now at a stage where interest rates seem to be rising and theres quite a bit of uncertainty about how far it will go before it stabilises again he said even a 12 percentage point increase in interest rates would have a big impact on japanese firms particularly those in the servicesector with low profits or high debt tan said theyve been used to a very low interest rate environment for quite a while so it is really the impact on the economy that could potentially have an impact on our ratings he said sp currently assigns an a longterm and a1 shortterm sovereign debt ratings on japan the outlook on the longterm rating is stable