Ratings agency Standard & Poor's says Ukraine will likely default on its debt if there are no significant improvements in the political crisis, which it does not expect.
The agency cited the increasing violence between protesters and police as it downgraded the country's rating by a notch to CCC.
Ukraine's government and the opposition are locked in a battle over the country's future. Several regions in the west are in open revolt, while many in eastern Ukraine back the president and favour strong ties with Russia, their former Soviet ruler.
Russia has an agreement with Ukraine's government to provide financial support, but has put that on hold pending the violence.
S&P says the violence "raises the uncertainty regarding the continued provision of Russian financial support over the course of 2014."