Labour's election results were "not nearly good enough", the party's former deputy leader has said.
Harriet Harman urged the party leadership to look to the success of newly-elected London Mayor Sadiq Khan, who "reached out beyond Labour's core base".
The party needs to be "doing better" if it has a chance of getting into government in 2020, she warned.
"I think we are all very clear that, although we are one point ahead of the Tories in the share of the vote in the elections - compared to we were seven points behind last year in the general election - that is not nearly good enough," Ms Harman told the BBC Radio 4 Today programme.
Jeremy Corbyn ordered his MPs to cut out public criticism of his leadership as he defended the party's recent performance at the ballot box at a meeting on Monday night.
The Labour leader directly confronted unrest in the ranks fuelled by last week's election results when he addressed the weekly gathering of his MPs and peers at Westminster.
He conceded that the party was "not yet doing enough" to win back power in 2020 and acknowledged the need to broaden the appeal of his message - but insisted things were moving in the right direction.
Mr Khan, whose victory in the London mayoral contest provided the Opposition with an eye-catching result, was greeted with cheers as he arrived at the Parliamentary Labour Party (PLP) meeting.
He warned that Labour risked missing an "open goal" unless it showed itself to be "a credible government-in-waiting" which focused on the issues and rejected an "us and them approach".
Ms Harman said Mr Khan had set out his stall to be mayor for all Londoners, not just core Labour supporters.
She added: "Obviously we need to be doing better and Jeremy Corbyn said that himself at the PLP last night. We need to be doing better if we are going to be able to get into government and put our policies into action."