Updated

European Central Bank head Mario Draghi is defending the bank's offer to purchase government bonds, saying it was key to defusing fears the eurozone might break up.

Germany's Constitutional Court will hear arguments challenging the program next week.

No bonds have been bought, but the mere offer has lowered bond-market borrowing costs for indebted countries such as Spain and Italy, lowering fears they might not be able to pay their debts.

Draghi rejected criticism that the bond purchase program took pressure off governments to reform their finances.

Draghi said in the text of a speech Monday in Shanghai that governments that want the help must meet strict conditions, or else reform without the help from the purchases. He said that "either way, they have to persevere in their reform efforts."