The source declined to reveal any details of the letter.
Last Friday, del Ponte circulated through Luxembourg's EU chair a letter among member-countries' foreign ministers, citing her arguments for the assessment that Croatia's cooperation with the UN court is not complete.
She said highly-placed networks in Croatia were protecting runaway General Ante Gotovina and that the government was ambivalent about his arrest.
Luxembourg Prime Minister Jean Claude Juncker said after talks with the chief prosecutor that the final decision on the start of Croatia's EU entry talks had not been made yet. He added the talks would start on March 17 only if Gotovina was transferred to The Hague by then, otherwise they would be postponed until Croatia met its obligation to fully cooperate with the tribunal.
France Presse, which received a copy of the Croatian Foreign Ministry reply from sources in Brussels, said today that in the letter bearing yesterday's date Foreign Minister Miomir Zuzul stated that Croatia would do "all in its power" to meet the "unavoidable obligation" to hand over Gotovina to the Hague tribunal. Zuzul did not pledge, however, that the issue would be closed by March 17.
Zuzul said the Croatian government would do "all in its power" to "fully cooperate with the Hague tribunal and its prosecutor" del Ponte so that Gotovina could be tried in The Hague.
Gotovina's arrest "remains an unavoidable obligation" for Croatia, "irrespectively of the decision" the EU made in December on the conditional start of entry talks with Zagreb on March 17, said Zuzul.
He underlined he was confident the Union would confirm that March 17 would be the start date of Croatia entry talks.