Ahmad Fawzi, spokesman for UN envoy al-Akhdar al-Ibrahimi, also said Shia cleric Ayat Allah Ali al-Sistani, who has been demanding early direct elections, appeared to accept that time was too short to organise proper polls before the handover.
"It's not a question of delaying [the handover]. It's finding a new timetable," Fawzi told BBC Radio 4.
"Elections will take place when the country is ready and that will be after the handover of power."
Al-Ibrahimi said the timing of elections should not be tied to a specific deadline, but the timing should be flexible to allow for good preparations.
"The timing should not be a prisoner to any deadline," al-Ibrahimi said. "We need to organise elections as early as possible but not as early as impossible."
Fawzi said he had attended Thursday's meeting between al-Ibrahimi and al-Sistani in Najaf.
"He [al-Sistani] seemed to accept the fact that three-and-a-half months were not sufficient to arrange and conduct elections," al-Ibrahimi's spokesman said.
"You need to put certain things in place before you can organise elections.
"There is a legal framework to be put in place, there's a political consensus that has to be reached before you can start the process of managing and organising an election," he added.
"Everything we have seen up until now indicates that it is unlikely that this country will be able to organise elections by that date," Fawzi said.
Caucus system rejected
In New York, diplomats said UN officials believed elections might be possible before the end of the year, but said a caucus system proposed by the US, at least in the form Washington had wanted, was no longer on the table.
"He (al-Sistani) seemed to accept the fact that three-and-a-half months were not sufficient to arrange and conduct elections"
spokesman for al-Akhdar al-Ibrahimi
However, the envoys believed some transfer of power would take place on 30 June, and not be delayed until after elections.
UN Secretary-General Kofi Annan sent al-Ibrahimi to Iraq to resolve the dispute over how to form a provisional government.
The White House, after scorning the world body for months, asked Annan to intervene when al-Sistani insisted on direct elections rather than caucuses for members of a national assembly that would choose an interim government.
Annan expects to give his recommendations on the election process before the end of the month.
Annan's spokesman, Fred Eckhard, said the secretary-general understood there was "a consensus emerging" for direct elections as a result of talks al-Ibrahimi had with various Iraqi leaders.
"There is wide agreement that elections must be carefully prepared, and that they must be organised in technical, security and political conditions that give the best chance of producing a result that reflects the wishes of the Iraqi electorate," Eckhard said.
"Everyone expects elections by 2005," he added.
"The question is what can be done before 30 June and, if it can't be elections, what other way can you find to establish a
legitimate government," he added.