Two senior officials, both United Russia members, have clashed head-on in Volgograd, where the city's mayor has refused to leave office after being fired by the governor and has threatened to sue.

The governor, Anatoly Brovko, cited  "violations of human rights" as the reason for the ouster, but a Volgograd representative in the State Duma said the conflict looked like a power game indicative of internal tensions in United Russia.

Brovko ordered the dismissal of Roman Grebennikov, 36, on Tuesday.

The governor did not elaborate on the human rights violations, but said in a statement carried on his administration's web site that he "had to make this decision in order to stabilize the situation … [because] it's no secret that Volgograd authorities have long exhibited inability or unwillingness to govern the city."

Grebennikov challenged his ouster, saying it was done with legal violations and aimed to disrupt the situation in the city.

"I hold that the governor's decision is illegal and amounts to an attempt to destabilize the situation in the regional center," Grebennikov said in a statement on City Hall's web site. "I will defend my position in court."

The dismissal order came when the mayor was on sick leave — which makes it illegal — and the decision was not approved by the city legislature, Grebennikov said.

Volgograd city lawmakers and federal authorities have kept silent on the matter, but the local branch of United Russia backed Brovko on Wednesday, proposing First Deputy Mayor Sergei Sokolov for acting mayor, Interfax reported.

Grebennikov was removed as head of Prime Minister Vladimir Putin's public office in the region last year, and he lost his post of deputy secretary of United Russia's Volgograd branch last week.

About 1,000 people rallied in Volgograd late Wednesday in support of the mayor, Gazeta.ru reported.

Grebennikov was elected Volgograd mayor in 2007 on the Communist Party's ticket but later joined United Russia. His term in office expires in spring 2012.

He has a history of clashes with the governor, who has accused him of ignoring court orders. Brovko sought the Kremlin's support to oust Grebennikov in January, but found none, Nezavisimaya Gazeta reported Monday, citing an unidentified source in the regional government. The Kremlin is displeased with Brovko and may remove him after the current electoral cycle ends in 2012, the source said.

But Grebennikov may also be in the federal authorities' bad graces, with Putin publicly scolding him during a trip to Volgograd in June for creating bureaucratic hurtles for real estate developers in the city.

The Prosecutor General's Office held a large-scale check into the activities of city authorities after Putin's visit and reported multiple violations, but the findings did not implicate the mayor directly.

A February survey by SuperJob.ru indicated that 70 percent of Volgograd residents thought local officials were underperforming at work. But Nezavisimaya Gazeta said Grebennikov is nevertheless the most popular United Russia representative in the city.

The clash shows splits in the ruling party, said Oleg Mikheyev, a Volgograd native and a Duma deputy with A Just Russia.

"If two members of the same party couldn't come to an agreement, that means the situation within United Russia is very complicated," he said by telephone Wednesday.

He also said Grebennikov's position was shaky.

"While Grebennikov has gained more support over time, his team remains weak," said Mikheyev, whom Nezavisimaya Gazeta identified as the second-most popular politician in Volgograd.

Early mayoral elections would have to be called if Grebennikov is ousted, but it remained unclear Wednesday whether they or a legal battle would proceed next.

Mikheyev, named by experts as a possible candidate for Volgograd mayor, refused to comment on the possibility of running, saying only that A Just Russia "has its own plans for the mayoral office."