FRANKFURT, Germany (AP) — European Central Bank head Mario Draghi says the bank's stimulus efforts need to be "persistent" even as the economy recovers and that any scaling back of support has to come gradually.

Draghi's said in a speech Tuesday at a conference in Sintra, Portugal, that "there are strong grounds for prudence" in adjusting the level of stimulus and that any withdrawal of stimulus "will have to be made gradually."

Market observers are watching for signals about when the ECB will start scaling back its 60 billion euros ($67 billion) per month in bond purchases, a step aimed at increasing inflation and growth.

Draghi said, however, that stimulus "is still needed" and that bank policy "needs to be persistent and we need to be prudent" about adjusting it.