David Miliband urged Labour delegates to ''look forward''
David Miliband has urged Labour to be optimistic about the future, insisting the Conservatives are "beatable".
The foreign secretary told the party conference he "hates defeatism" and said tough times in government were still better than being in opposition.
Mr Miliband paid tribute to Gordon Brown, saying he had made a huge difference on the international stage.
Mr Miliband, seen as a potential challenger to Mr Brown, chatted and joked with the PM after his speech.
There has been persistent speculation about Mr Miliband's intentions after he wrote a newspaper article in July suggesting Labour needed to raise its game if it wanted to win the next election.
Hope not despair
Some interpreted this as a signal that he was positioning himself to take Mr Brown's job as muttering about his leadership grew.
BBC political editor Nick Robinson said nothing in the text of the speech was openly disloyal, but "everything about it declared 'I'm here if you want me to lead you'."
In his speech to Labour delegates, Mr Miliband, who has denied any plans to challenge Mr Brown, said the party must "defeat fatalism" and "replace it with hope".
"The truth is these Tories are beatable," he said. "Let us say with conviction they are beatable."
Labour must look to the future rather than the past, Mr Miliband stressed, while remaining focused on its core values.
He praised Mr Brown's commitment to reducing global poverty and the key role he played on securing an international agreement on prohibiting the use of cluster bombs.
"That is the sort of difference he makes in the world," said Mr Miliband.
The foreign secretary finished by urging the party to "take pride not in what we have finished but what we have started".
"Together, let us earn the privilege, seize the opportunity, and prove the fatalists wrong."
Gordon Brown and David Miliband share a joke on the conference stage
On international matters, Mr Miliband defended the UK's military role in Iraq and Afghanistan, saying its continuing presence in the two countries helped people there to live "free of fear".
In the aftermath of Saturday's bomb attack in Islamabad, Mr Miliband promised the UK would stand "shoulder to shoulder" with the Pakistani people to confront the "evil" of terrorism.
On Zimbabwe, he said the government would be "resolute" in its support for the Zimbabwean people as they strive to end the era of "one-party rule" by Robert Mugabe.
And he warned Russia about any attempts to destabilise the Georgian government after their recent conflict.
He urged Labour to remain "engaged" in international institutions, particularly in Europe, and accused the Conservatives of "distancing" themselves from both the EU and the US.
"Now is the time to be out there, engaged, arguing for our values, putting them into practice," he said.