Jeremy Corbyn has promised to give more decision-making power to rank-and-file Labour members after being decisively re-elected as party leader on the back of their votes.
Mr Corbyn told the Observer that his emphatic 62%-38% victory over challenger Owen Smith was a "vindication" giving him a "very strong" mandate to lead.
His comments came as London mayor Sadiq Khan warned that a failure to unite after the bruising leadership contest could kill off Labour forever.
Speaking as Labour's annual conference opened in Liverpool, Mr Khan told the Sunday Times: "We know from history - the Gang of Four in the 1980s - that when the Labour Party splits, we are out of power for a generation.
"Now it is far more serious than that. If the Labour Party splits, it could be the end of the Labour Party."
As Mr Corbyn sought to reach out to disaffected backbenchers in the wake of his re-election, one route by which it had been thought that senior moderates could return to his shadow cabinet seemed to be running into the sand.
A meeting of the party's ruling National Executive Committee failed to make progress on Saturday night on proposals - backed by MPs and deputy leader Tom Watson - for elections to the shadow cabinet.
It was thought that the move would allow former frontbenchers who quit in protest at Mr Corbyn's leadership in June to rejoin his parliamentary top team without losing face by claiming they were doing so with their own mandates.
But Mr Corbyn has set his face against the idea, while suggesting that members in the country could be given a role in picking shadow cabinet members.
Speaking to The Observer, Mr Corbyn said: "I have been given the authority by the members and that is what I intend to deliver on."
With party membership swollen to more than 500,000 - and new recruits overwhelmingly backing his leadership - he said: "The participation is even higher, and my majority is bigger, and the mandate is very strong. So let's use it to reach out.
"With this huge membership, that has to be reflected much more in decision-making in the party."
Mr Corbyn has been meeting key Labour MPs - including Parliamentary Labour Party chairman John Cryer and popular backbencher Jess Phillips, who chairs the women's PLP - as he seeks to rebuild his frontbench team in a reshuffle expected soon.
He used his victory speech to issue a call for Labour MPs to "work together and respect the democratic choice that's been made". But critics said he should extend an olive branch by allowing MPs to elect the shadow cabinet and stamping out any threat of de-selections for those seen as disloyal.
Mr Smith, who quit as shadow work and pensions secretary to fight for the leadership, said he would "reflect carefully" on what role he could play in Labour's future, but urged moderate MPs not to split the party.
But Jewish peer Lord Mitchell indicated he would make good on his earlier promise to quit the party if Mr Corbyn remained.