The two prime ministers met just hours after European Enlargement Commissioner Olli Rehn said in Brussels that "if the Commission were to give its recommendation on the basis of today's information, I could not recommend opening negotiations with Croatia."
"I expect the negotiations to start on March 17 as decided by the European Council in December last year," Sanader said at a joint press conference with Juncker, whose country currently holds the EU presidency.
Sanader said he was "not concerned, but surprised" by Rehn's statement, which he said reflected the criticism directed by some European partners at Croatian authorities over their failure to arrest fugitive Croatian army general Ante Gotovina, who is sought by the UN war crimes tribunal in The Hague.
Sanader reiterated that the Croatian government had proved it was cooperating with the Hague tribunal.
Sanader said he would meet European Commission officials "this evening or tomorrow" to see what information Rehn's assessment was based on. He denied Rehn's statement that the Croatian government had initiated negotiations with Gotovina on his voluntary surrender.
"I don't know what Mr Rehn meant by that, but it's not true," the Croatian prime minister said. He called on "anyone in Europe" having any information in connection with the runaway general to inform the Croatian government.
Juncker said he was "fully confident" that his Croatian counterpart was ready for full cooperation with the Hague tribunal, adding that he would discuss the issue with the tribunal's chief prosecutor, Carla del Ponte.
Del Ponte is expected to present her assessment of Croatia's cooperation with the tribunal in Brussels on Thursday. Her assessment will be important for a decision of the European Council, which is due to endorse the European Commission's negotiating framework in February.
I am optimistic that the talks will start as announced, but I have to discuss it with other governments, Juncker said.
Sanader said that today's meeting of Justice Minister Vesna Skare-Ozbolt in The Hague was a routine meeting to present a report on Croatia's cooperation with the tribunal.