So far just 272 refugees have been moved to other countries out of the 160,000 that European Union nations agreed to relocate as the continent faced a wave of people fleeing conflict in Syria and elsewhere.
"It's not the commission that has not delivered," Juncker, the head of the executive branch of the 28-nation union and the driving force behind the plans, told a press conference.
Juncker vowed not to abandon the relocation scheme, which was finally approved in October over the opposition of several eastern European capitals, to move some asylum seekers from frontline countries Greece and Italy.
He said he was "getting a little tired" that the commission was coming under fire for not doing enough to resolve the worst migrant crisis since World War II when it has spent months drawing up joint relocation and other plans.
He excoriated member states for struggling to implement plans they had themselves agreed on, warning that the EU was "moving toward a serious crisis in terms of credibility" if they don't assume their legal and political responsibilities.