The nominations still require endorsement at the party's ongoing five-yearly congress, but add weight to speculation of a political exit for Nguyen Tan Dung, the pro-business premier widely considered a modernizer and credited with a wave of recent moves to liberalize the fast-growing economy.

Dung, 66, was until recently widely tipped by diplomats and analysts to become the next party chief, which could have strengthened the hand of his progressive faction.

His exit could slow the momentum of further reform, although experts say there is still an outside chance for him to mount a fightback during the congress by calling on his support among the wider party.

During an interview with some local media on Sunday, Vu Trong Kim, Vice President and General Secretary of the Vietnam Fatherland Front, confirmed leaked reports that a recent party meeting had nominated incumbent General Secretary Nguyen Phu Trong, 71, to extend his tenure and Dung had withdrawn from the contest when the politburo was agreeing its candidates.

An audio recording of the comments was heard by Reuters in which Kim, a member of the outgoing central committee, praised Dung and said there was 100 percent politburo support for Trong.

Public comments from the party on internal politburo processes are rare in Vietnam.

"I very much welcome comrade Nguyen Tan Dung and some other comrades in the politburo who voluntarily withdrew from being nominees to gather credit for comrade Nguyen Phu Trong," Kim said.

Slim chance

Normally considered a stale, procedural affair, the current congress has attracted a buzz of excitement and social media speculation in Vietnam about the possibility of a leadership showdown during a drawn-out and secretive internal election.

Kim confirmed the agreed nominations, besides Trong, were Minister of Public Security Tran Dai Quang for president, Dung's deputy, Nguyen Xuan Phuc, for prime minister and Legislative Vice-Chairwoman Nguyen Thi Kim Ngan to head the National Assembly.

Some experts and diplomats familiar with the arcane inner workings of the Communist Party believe Dung's popularity and cultivation of broad party backing means he could be put back in contention, should he choose to fight.

Dung would need to be nominated during the congress to become a new central committee member, but to stand a chance of becoming leader he would have to decline that nomination, they say. The 1,510 congress delegates could then vote to reject his attempt to withdraw, thus keeping him in the race.

Dung's office did not respond to a request by Reuters for comment.

Analysts say Dung is an ambitious figure, decisive in implementing policy and his exclusion ahead of the congress suggests concerns among the party's old guard that he could test Vietnam's traditional consensus leadership model.

Edmund Malesky, an expert on Vietnamese politics at Duke University, said congress was not scripted and key to any outcome was a central committee "way more powerful" than those of other communist states.

"The question is whether Dung wants it... He's not going to come out and say it in an obvious way," he said.

"He himself has benefited from the influence of the central committee, and we know that he's capable of mobilizing votes ... if he decides he wants it, then this is a real possibility."

By Martin Petty - Reuters - January 24, 2016

Vietnam's Communist Party boss 'to run unopposed'

The General Secretary of Vietnam's Communist Party, Nguyen Phu Trong, will be the only candidate for the post at a party congress, state media report.

It means his main rival - reformist PM Nguyen Tan Dung - has little chance of taking the leadership role, they say.

But complicated voting procedures mean another candidate could still be named before the congress ends on Wednesday.

Conservatives, led by Mr Trong, are concerned that Vietnam is abandoning its socialist past under Mr Dung.

During his 10 years in office Mr Dung has driven the reforms which have seen Vietnam grow quickly as it has been integrated into the global trading economy, reports the BBC's Jonathan Head from the Vietnamese capital Hanoi.

However, he adds, the speed of the reforms and rising corruption have been criticised by the conservative camp. Key appointments

The Communist Party congress - which is held every five year in the one-party state - is meeting in Hanoi.

Behind closed doors, the 1,510 members will nominate the party's general secretary and the next president and prime minister.

Mr Dung is seen as modern, and friendly towards the US. He has also gained popularity domestically with strong anti-China rhetoric when it comes to disputed territory in the South China Sea.

Mr Trong is seen to be more friendly towards China - Vietnam's largest trading partner. How new leaders will be chosen:

- Delegates will elect a new central committee

- On one of the last days of the congress, the new central committee will meet to select a 16-member politburo from among its ranks

- From within the politburo a general secretary, prime minister and president will be nominated

- The general secretary will need approval from congress

- The prime minister and president will be approved by the national assembly in about six months time - however this is normally just a rubber stamp

BBC News - January 24, 2016