Jeremy Corbyn has appeared in a campaign video for Rebecca Long-Bailey, in an apparent show of support for her bid to replace him as Labour leader.
In the video, posted on Twitter, Mr Corbyn promised he would give the shadow business secretary his “absolute support” if she wins the contest.
He has not appeared in campaign videos for her leadership rivals, Sir Keir Starmer and Lisa Nandy.
Members began voting earlier this week, with the result announced on 4 April.
Mr Corbyn has also appeared in campaign video for shadow justice secretary Richard Burgon, one of five candidates for the deputy leader position.
In the video, he said there was “a lot of merit” in Mr Burgon’s proposal to give party members a vote on whether a future Labour government should take part in military action, in certain circumstances.
Mr Corbyn did not offer an explicit endorsement of either Mrs Long-Bailey or Mr Burgon in his appearances in their respective campaign videos.
He said last month that he would not be revealing which of his potential successors he would be voting for.
Asked in the video which issues she thinks will come up at the next election, Mrs Long-Bailey replied: “I think the next general election will be a climate election.”
She adds that it will be important to make Labour’s plans for a “green industrial revolution” a “central part” of the party’s offer to voters.
Last week Mr Corbyn, who is standing down after the party’s heavy election defeat, said he would consider serving in the shadow cabinet if offered a job by his successor.
Mrs Long-Bailey has said she would offer him a place in her top team if she is successful, and has previously scored his leadership of the party as “10 out of 10”.
Her candidacy has been backed by key allies of Mr Corbyn, such as shadow chancellor John McDonnell and shadow home secretary Diane Abbott.
In an interview with the i news website on Thursday, Mrs Long-Bailey sought to distance herself from a charge made by her critics she is the “continuity Corbyn” candidate.
“If I’m a continuity socialist, then fine I will accept that title, but there is no such thing as Corbynism.”
Mrs Long-Bailey revealed earlier this week she had received £120,000 in donations from Momentum, the campaign group which supported Mr Corbyn’s bid for the party leadership in 2015.
In figures published on her campaign website, she also declared £200,000 in support from trade union Unite, led by another Corbyn ally, Len McCluskey.
Wigan MP Ms Nandy has disclosed a series of recent donations on her website, the biggest of which was £25,000 from the GMB trade union.
The Young Labour national committee, which is backing Mrs Long-Bailey for the leadership, wrote to all leader and deputy leader candidates on Thursday, urging them to publish all donations to their campaigns to ensure party members are fully informed about who is bankrolling them.
All candidates, including Sir Keir, the party’s Brexit spokesman, have also been declaring support in the Commons Register of Members’ Interests.
By 10 February, when the register was last updated, Sir Keir had recorded a series of small donations from Unison, a union backing his campaign, totalling just over £8,000.
The most recent recorded donation he has registered was accepted on 24 January. He has not posted any more recent donations on his website.
A spokesman for his campaign said a more recent batch of donations had been submitted to Parliament and they expected it to be published next week.
Voting in both the leadership and deputy leadership contests works using a preferential system, with members ranking the candidates in order of preference.
If one fails to get more than half the first preference votes, the second preference votes of the lowest-ranked candidate are redistributed until the contest produces a winner.
As well as Mr Burgon, shadow education secretary Angela Rayner, shadow equalities minister Dawn Butler, Edinburgh South MP Ian Murray, and Tooting MP Rosena Allin-Khan have all made it through to the members’ ballot for the deputy leadership.
Ms Rayner is regarded as the frontrunner in that contest, and has the most support from local Labour branches as well as unions and affiliate groups.