By  Ira Iosebashvili and  Josie Cox 

The euro slid to its lowest level against the dollar in 14 months on Thursday, after the European Central Bank unexpectedly cut its main policy rates and announced additional measures aimed at boosting the region's sagging economy.

In a statement accompanying its decision, the central bank said it was trimming the main refinancing rate to 0.05% from 0.15% and the deposit rate to -0.2% from -0.1%. ECB President Mario Draghi said at a news conference that the ECB would start buying asset-backed securities and covered bonds in a further bid to stimulate growth, and that the governing council had discussed the implementation of a program of broad-based asset purchases, known as quantitative easing.

The euro was recently down 1.5% to $1.2949, its lowest level against the dollar since July 2013, and on track for its steepest drop against the greenback since November 2011.

Investors selling the euro to buy the dollar pushed the buck up to a nine-month high of ¥105.37 against the Japanese yen. The euro lost 1.2% against the yen to trade at ¥136.17.

The ECB's move surprised market watchers, many of whom believed the central bank would wait several months before further easing monetary policy, to give measures taken earlier in the year time to take effect. It also highlighted the effect that divergent monetary policies in the U.S. and eurozone is likely to have on the dollar and euro. While the ECB is expected to continue on an easing path, many analysts expect the Federal Reserve will raise rates in the middle of next year, making the greenback a more attractive proposition than the euro for yield-seeking investors.

While data in the U.S. show a recovery that is gaining traction, "the eurozone is stuck in the mud right now," said Carl Forcheski, director of foreign exchange at Societe Generale. "The overall direction for the euro appears to be lower."

The ECB in June became the largest central bank to experiment with a negative rate on bank deposits, a measure aimed at encouraging banks to lend surplus funds to other financial institutions rather than parking them at the ECB.

Poor data in recent weeks, however, have repeatedly underscored the sluggishness of the eurozone's economic recovery, fanning recessionary fears and heaping pressure on the central bank to take further stimulus measures.

In other currencies, the British pound lost 0.7% against the dollar to trade at $1.6344, its lowest level since early February. The Bank of England left its benchmark interest rate unchanged Thursday as officials led by Gov. Mark Carney await signs that Britons' earnings are to set to rise.

--Write to Ira Iosebashvili at ira.iosebashvili@wsj.com and  Josie Cox at josie.cox@wsj.com