Sir Keir Starmer has warned warring factions within Scottish Labour that “divided parties don’t win elections”.
Speaking on his first visit to Scotland since becoming UK Labour leader, Sir Keir insisted that Scottish Labour leader Richard Leonard still had his support.
The two leaders held face-to-face talks on Thursday afternoon.
Mr Leonard has been facing calls to quit from several of his own MSPs, but has refused to do so.
He had been due to face a confidence vote at Scottish Labour’s ruling body last weekend.
But the motion was withdrawn at the last minute after being discussed by the Scottish Executive Committee (SEC).
Mr Leonard’s critics claim the party faces disaster at next May’s Scottish Parliament election unless he goes - but he and his allies have accused them of sabotage, and insist he is the best person for the job.
Scottish Labour is largely divided between left-wingers such as Mr Leonard, who was a close ally of Sir Keir’s predecessor Jeremy Corbyn, and centrists who believe the party needs a change of direction if it is to survive.
It has led to speculation that Sir Keir would be happy to see Mr Leonard go - although he has always strongly denied this.
During his visit to Edinburgh, Sir Keir told BBC Scotland: “I work closely with Richard and we speak frequently - we are meeting this afternoon and we are talking about the job that we have to do.
“He has got my support and I am working with him and that is why I’m here to have a face to face visit, but I talk to Richard regularly on the phone.”
When asked what he would say to those who have been calling for Mr Leonard to stand down, Sir Keir said his aim as leader was to “unite the party and bring people together”.
He added: “That is among the reasons that I’m here today, because we need a united party here in Scotland and we need a united party across the United Kingdom.
“Parties that are divided do not win elections”.
‘Job in hand’
Sir Keir went on to claim that the “vast majority” of people across the UK were tiring of a “government in Westminster that is increasingly obsessed with Brexit, and the SNP that are talking only about independence”.
He said politicians should instead “focus on the job in hand, which is dealing with the pandemic and working together to that end”.
Scottish Labour is the third largest party at Holyrood behind the SNP and Conservatives - with opinion polls currently suggesting it is unlikely to improve its fortunes in next year’s election.
The party lost all but one of its MPs in last year’s general election after finishing fifth in the European Election a few months earlier.