The Standard & Poor's Ratings Services has downgraded Tunisia's government credit rating due to the persistent political instability in the country.

The move Tuesday is the latest blow to the country's economy, which has been suffering since Tunisians overthrew their dictator in January 2011, as well as due to Europe's financial crisis.

S&P lowered Tunisia's rating to BB- from BB with a negative outlook. It is the third such downgrade since the uprising.

In justifying its move, the agency cited the ongoing political crisis in the country following the assassination of leftist politician Chokri Belaid on Feb. 6.

Tunisia's political parties are in negotiations to form a new government after a proposal by Prime Minister Hamadi Jebali to form a technocratic cabinet was rejected Monday.