Latvia was the worst-performing EU economy at the end of 2008
Latvia's sovereign debt has been cut to junk status as its economy struggles with the financial crisis.
The credit ratings agency Standard & Poor's has reduced its rating to BB+/B, which is below investment grade.
S&P predicted that Latvia's economy would contract by 12% this year, following its 4.8% decline in 2008.
The Baltic nation was once the fastest growing economy in the European Union, but in the last three months of 2008 it was the worst-performing.
"The downgrade of Latvia reflects what we consider is a worsening external outlook and the associated implementation risks on the government's ambitious economic programme," said S&P credit analyst Eileen Zhang.
The country was forced to seek a 7.5bn-euro ($9.6bn; £6.7bn) bail-out from the International Monetary Fund in December, after nationalising its second-biggest bank.