Standard & Poor's Rating Services said it had revised its outlook on Sofia from stable to positive, based on improving revenue autonomy and better-than-expected budgetary performance.

S&P also affirmed the 'BB+' long-term issuer credit rating on the city, CNN said

The rating was constrained by Sofia's weak institutional framework, low expenditure and revenue flexibility and potential pressures associated with non-self-supporting entities, S&P said.

These factors were partially mitigated by a high economic growth, which resulted in increasing revenues, improving budgetary performance and a modest debt, S&P said.

S&P said it expected that the city could significantly improve the quality of local infrastructure without a large debt accumulation through improved tax autonomy, gradual absorption of EU funds and high economic growth, Thompson Financial News said.