European Commission head Jean-Claude Juncker said Thursday "challenging" negotiations with Greece would continue, jafter late night talks with premier Alexis Tsipras broke up without a deal.

"I was sleeping three hours after having had long challenging discussions and negotiations with the Greek prime minister," Juncker told a committee hearing at the European Parliament.

"This is the reason why I have to leave (the hearing)... We have to prepare the next round of negotiations," he said.