NAYPYIDAW (AFP) - Myanmar's reformist President Thein Sein was re-appointed Tuesday as head of the ruling party at a key meeting aimed at reviving its flagging political fortunes against a resurgent opposition.

Lower House Speaker Shwe Mann, a fellow reformer who had been tipped to replace Thein Sein, was picked as acting chairman to handle the day-to-day business in a party vote, members said. Thein Sein relinquished an active role within his Union Solidarity and Development Party (USDP) to become president of the country last year at the end of nearly half a century of outright military rule.

Analysts say Thein Sein has been locked in a power struggle with Shwe Mann, who was more senior under the previous military regime and is widely considered to harbour ambitions of taking over the presidency.

After a military career spanning almost half a century, Thein Sein seemed an unlikely champion of democratic reform when he was installed as president by the army and its allies last year.

A key figure in an army that ruled the nation with an iron fist for nearly half a century, he had a reputation for staunch loyalty to ex-junta strongman Than Shwe. Since taking office in March 2011, Thein Sein has overseen dramatic changes such as the release of political prisoners, the parliamentary debut of opposition leader Aung San Suu Kyi and ceasefire pacts with ethnic rebels.

But his government has also presided over an ethnic conflict in northern Kachin state as well as sectarian bloodshed in western Rakhine, where security forces were accused of opening fire on Rohingya Muslims in June 2012. A son of farmers, born in a small village in the southern Irrawaddy region, Thein Sein began his army career at the military academy, developing a reputation as a bureaucrat in uniform rather than a combat soldier.

As junta prime minister, he became a target of outrage at the generals' reluctance to allow outside aid to victims of a cyclone in 2008 that left more than 138,000 people dead or missing.

Many party members had said before the vote they expected Shwe Mann to be named USDP chairman, as the party looks towards a 2015 election seen as a major test of the regime's democratic credentials. MPs said the unexpected outcome aimed to prevent friction between the government and the ruling party.

"To have good relations between the executive and the party we have to keep the positions of the ministers and the president the same" within the USDP, said a party member who did not want to be named.

"If we change too much, relations between the government and the party will be difficult."

The USDP is still smarting from a heavy defeat in April by-elections at the hands of Nobel Peace Prize laureate Aung San Suu Kyi and her National League for Democracy (NLD) party, which won 43 of the 44 seats it contested.

The USDP swept a general election two years ago that was marred by allegations of fraud and the absence of Suu Kyi, who was under house arrest at the time.