WASHINGTON (AP) — The credit rating agency Moody’s Investors Service has lowered its outlook on the U.S. government’s debt to “negative” from “stable.”

In a statement Friday, the agency cited the cost of rising interest rates and political polarization in Congress for its move.

Moody’s retained its top triple-A credit rating on U.S. government debt, though it is the last of the three major credit rating agencies to do so.

Fitch Ratings lowered its rating to AA+ from AAA in August, and Standard & Poor’s downgraded the U.S. in 2011.

A reduced outlook, however, raises the risk that Moody’s could eventually strip its triple-A rating from the U.S. as well.