Turkish President Recep Tayyip Erdogan arrives at the 2018 NATO Summit at NATO headquarters on July 12, 2018 in Brussels, Belgium.

Standard & Poor's took Turkey's sovereign debt rating even lower on Friday.

S&P had already rated Turkey's bonds as "junk," but on Friday lowered the the long-term foreign currency sovereign credit rating one notch to a "B+" and the long-term local currency rating to "BB-". The credit rating firm also forecast a recession for Turkey next year.

"Over the last two weeks, the Turkish lira has exhibited extreme volatility," the rating agency said in a statement Friday. "This follows Turkey's prolonged economic overheating, external leveraging, and policy drift."

A "junk" bond is anything rated "BB" or lower by the agency, and is considered a high-risk investment. A bond credit rating indicates its credit-worthiness, and helps investors asses whether or not the debt will be repaid.