The European Central Bank cut interest rates on Thursday to boost the euro zone economy, surprising financial markets by dropping its main refinancing rate to zero from 0.05 percent.It also expanded its quantitative easing asset-buying programme to 80 billion euros a month from 60 billion euros and cut its deposit rate to -0.4 percent from -0.3 percent, charging banks more to keep their money with the ECB.The moves - which knocked the euro down 1 percent against the dollar - reflect the ECB's struggle with falling inflation expectations and worries about ultra low price growth.Attention now turns to ECB President Mario Draghi's 1330 GMT news conference.