Serbia and Kosovo have failed to agree on how to implement a deal normalizing their relations, European Union officials said Wednesday, less than three weeks after the two sides were internationally hailed for the breakthrough, dpa reported. "I can confirm that the implementation plan was not agreed," said Maja Kocijancic, a spokeswoman for EU foreign policy chief Catherine Ashton. "Implementation of the agreement is key, but that needs to bed one by Belgrade and Pristina. " Ashton brokered the normalization deal between the two sides,which was to open the door for closer ties with the EU for bothSerbia and its mostly ethnic Albanian former province. EU officials have warned that they expected "determination" inimplementing the agreement by June, when EU leaders will decidewhether to open talks with Serbia on accession and with Kosovo on anassociation deal. "We are continuing with the efforts," Kocijancic said.