David Miliband rallying call: Ed's a great leader
David Miliband has issued a rallying call to the Labour conference, saying the party now had a "great leader" in his younger brother Ed.
The shadow foreign secretary, long favourite for the top job, said "I'll be fine" before calling for party unity and getting a standing ovation.
He has yet to say whether he will serve in his brother's shadow cabinet.
Ed Miliband has said that his brother has a "huge amount" to give to the party and British politics.
David Miliband has said he is talking to colleagues about his future, and wanted to take his time to make sure he made the right decision - with no decision until after the conference.
"I don't know if you noticed but I came here on Saturday planning a slightly different week. I am now thinking what I am going to do instead," he told reporters ahead of the speech.
BBC political editor Nick Robinson said a friend of Mr Miliband told him he was considering not running for the shadow cabinet and could quit politics, although colleagues insist he has yet to make up his mind.
Asked about his brother's future on Monday, Ed Miliband said he would make his decision "in his own way and in his own time" but praised his "loyalty to me and the country".
"He has a huge amount to offer our politics," he added.
The two brothers met in private for nearly 10 minutes on Monday but it is understood they did not discuss David's future.
Nominations have opened for the 19 shadow cabinet posts, to be elected by a ballot of MPs, but it is unclear whether David Miliband will put himself forward by Wednesday's deadline.
Ed Miliband will allocate posts to the successful candidates after the vote on 7 October and he has insisted that decisions about who will get what job must wait until then.
In a speech on Monday, David Miliband told activists in Manchester that he had been "honoured and humbled" by the support he had received since narrowly losing the leadership election.
He urged the party to unify around his brother, saying he was "incredibly proud" of him.
"We have got a great new leader and we all have to get behind him," he told party supporters.
While he was proud of the campaign that he had fought, he said that no-one should enter such a high profile contest unless they were reconciled to the possibility of defeat.
Labour's task at the conference was to begin its "fightback", he added, and to show that it was focused on the country's future as well as its own.
There must be "no more cliques, no more factions and no more soap opera" within the party, he said, arguing that "unless we are united, we will lose".
Shadow health secretary Andy Burnham, who came fourth in the leadership contest, is among senior figures to have urged David Miliband to stay in frontline politics, saying "he hoped he stays as part of the team".
Former minister Vera Baird told BBC Radio Four's World at One that it would be "helpful" if David Miliband became shadow chancellor to ensure Labour continued to support the four-year plan for halving the deficit it endorsed at the election.
But ex-Treasury minister Geoffrey Robinson said Ed Balls - who has argued for a slower approach to reducing borrowing - was the "outstanding candidate" for that crucial position.
Although David won a higher percentage of votes from Labour MPs, MEPs and party members, Ed Miliband's success with trade union members and affiliated societies pushed him into first place in the leadership contest.
At a fringe meeting, former chancellor Alistair Darling said there was a case for reviewing the way Labour elected its leader, but stressed the party must unite around Mr Miliband.
"I do think that one of the oddities of our system was that even though the turnout in the union section was quite low, very low, in fact, its proportion in the electoral college is a lot higher," he said.
"So there may well be a case for asking ourselves whether this is the right thing."
The party has revealed that nearly a tenth of the votes cast - more than 36,000 out of 375,000 - were spoiled.
A spokesman said many voters had failed to comply with "clear" instructions to tick a box confirming they were Labour supporters.
But Derek Simpson, joint general secretary of the Unite union, whose governing body recommended that members back Ed Miliband, said: "It's being portrayed as just getting the union votes. But, in fact, Ed got 175,000 votes to David's 147,000.
"It was individual union members. All the candidates attended hustings meetings, and there were many of them over the campaign."
Mr Simpson also told BBC Radio 4's Today programme that the leaderships of some large unions, including Usdaw and Campaign, had supported David Miliband.