FRANKFURT (REUTERS) - The European Central Bank left interest rates unchanged as expected on Thursday, holding them at record lows as it prints money to lift the economy and raise inflation.

The decision to leave rates on hold was expected by all 60 analysts polled by Reuters after the ECB cut its deposit rate deeper into negative territory last month as inflation prospects soured further.

At Thursday's meeting, the ECB kept its rate on bank overnight deposits, generally seen as its primary interest rate tool, at -0.40 per cent.

The main refinancing rate, which determines the cost of credit in the economy was unchanged at 0.00 per cent while the rate on the marginal lending facility - or emergency overnight borrowing rate for banks - remains at 0.25 per cent.

The ECB will begin purchases of euro zone corporate bonds in June, its President Mario Draghi said on Thursday.

Speaking at a news conference after the ECB left interest rates unchanged, Mr Draghi said full details of the corporate bond purchase scheme would be given later on Thursday.

The ECB said last month it would start buying corporate bonds issued by companies that are based in the euro zone, have an investment-grade rating and are not banks.

Chief economist Peter Praet has said the ECB might follow a market index when choosing which corporate bonds to buy alongside government debt under its 80 billion euro (S$121.43 billion) a month asset-purchase programme.

The plan has raised questions about the risks the ECB will take onto its balance sheet by buying unsecured private debt.

The beneficial impact of these purchases on inflation has also been questioned given the limited size of the euro corporate bond market and its tenuous tie to the broader European economy.