Welsh First Minister Rhodri Morgan has announced he is backing Harriet Harman to be Labour's deputy leader.
Rhodri Morgan (R) says Ms Harman would work best with Gordon Brown
Mr Morgan said it was not a criticism of his working relationship with Welsh Secretary Peter Hain.
Mr Morgan told BBC Radio Wales that he thought the justice minister was "best suited to work as a team with Gordon Brown".
Mr Hain is among six contenders to replace John Prescott, with the result announced on 24 June.
The six hope to be deputy to Mr Brown, who will take over the party leadership on 27 June.
Mr Brown will also become prime minister, and he will decide whether the party deputy leader also becomes deputy prime minister.
Mr Morgan said "I think she (Ms Harman) is the right person to be a partner as deputy Labour leader and presumably deputy prime minister as well - although that's up to Gordon - with Gordon Brown.
Asked if this meant he was not impressed with Mr Hain, Mr Morgan said: "I certainly have not said that - I have an extremely good working relationship with Peter Hain".
Mr Hain was said to be "very relaxed" about Mr Morgan's decision to back his rival.
The Neath MP issued a statement saying he and the first minister have had "an excellent working relationship" and would continue to do so.
Two of Mr Morgan's ministers, Jane Davidson and Jane Hutt, are also backing Ms Harman, and his wife and Cardiff North MP Julie Morgan, is one of five Welsh Labour MPs who nominated her for the deputy's role.
Former Labour leader Neil Kinnock and his wife, Wales MEP Glenys Kinnock, are also in the Harman camp.
Mr Hain, meanwhile, has the public backing of another Welsh assembly minister, Carwyn Jones, as well as six other AMs.
Mr Hain also has the support of 15 Welsh MPs including Nick Ainger, Ann Clwyd, Sian James, Albert Owen and Don Touhig.
Of the other candidates, Jon Cruddas was nominated by MPs Martin Caton, Paul Flynn, Nia Griffith and Dai Havard, while Education Secretary Alan Johnson was backed by MPs David Hanson, Alun Michael and Alan Williams.
Labour chairman Hazel Blears has the support of Martyn Jones, with Kim Howells nominating International Development Secretary Hilary Benn.
All six deputy candidates and Gordon Brown were in Cardiff for the Welsh hustings on Saturday.