BOSTON (AP) — The credit ratings agency Standard & Poor's has downgraded its assessment of Russia's ability to repay foreign debt, signaling rising prospects that Moscow will soon default on external loans for the first time in more than a century.

S&P Global Ratings issued the downgrade to "selective default" late Friday after Russia arranged to make foreign bond payments in rubles on Monday when they were due in dollars. It said it didn't expect Russia to be able to convert the rubles into dollars within the 30-day grace period allowed.

S&P said in a statement that its decision was based par...