Kiev  - Masked government agents broke into the headquarters of Ukraine national natural gas company Naftogaz Ukrainy on Wednesday to search the premises, with the country's national intelligence agency SBU saying the raid was part of an anti-corruption action.

The armed men wore black combat uniforms commonly used by Ukrainian special force police and military units, witnesses said.

The SBU assault teams totalling 20-30 troopers were moving through Naftogaz offices searching for unidentified documents, they said.

A short tussle took place after a group of MPs loyal to Naftogaz management attempted to push through a cordon of SBU agents and remove the troopers' black masks.

Cursing and shouting could be heard from the corridor where the fracas took place. There were no injuries.

An SBU officer placed senior Naftogaz accountant Maria Kushnir under arrest. She was initially unable to leave the building because of a sudden heart problem, but later an ambulance took her to a local hospital under SBU escort.

The incidents came only hours after Ukraine's secret police the SBU arrested a senior tax administration official for allowing some 13.7 billion cubic metres of natural gas of disputed title and held in Ukrainian reservoirs and pipelines to be marketed in Ukraine.

The SBU was in the process of investigating a suspected secret agreement between Naftogaz officials and Ukrainian industry managers to sell the gas worth some 3.9 billion dollars, according to a morning SBU statement.

Naftogaz officials said they had received a court order arresting all gas controlled by the company - according to them an instruction if put into effect that would halt natural gas deliveries to Ukrainian and foreign customers.

Ukrainian President Viktor Yushchenko and Prime Minister Yulia Tymoshenko are locked in a bitter battle for control of the country's natural gas reserves. They have accused each other of attempting to use the massive cash stream generated by natural gas sales to advance their political careers.

Tymoshenko has argued the 13.7 billion cubic metres of gas are rightful property of the Ukrainian company Naftogaz, after the former owner, a Swiss intermediary company called RusUkrEnergo, lost title to the fuel after its contract to ship gas through Ukraine ran out at the end of 2008.

The parliamentarians arriving on the scene at the Naftogaz office and involved in the dust-up with the SBU agents were largely members from Prime Minister Tymoshenko's political party the Block of Yulia Tymoshenko.

Yushchenko's office in a Wednesday statement called Tymoshenko's arguments "grounds for the anti-corruption investigation," and repeated past declarations that RusUkrEnergo would receive full payment for the gas.

Tymoshenko has argued the potential income from the gas sale is critical to the survival of cash-strapped Naftogaz Ukrainy, and that the Yushchenko government opposes taking the gas from RusUkrEnergo because RusUkrEnergo secretly supports Yushchenko's political party.

Yushchenko last week said energy title in Ukraine should be subject to the rule of law, and denied illicit funding sources to his political party.

Conflict between Yushchenko and Tymoshenko over Ukraine's natural gas priorities sparked an two-week energy crisis in Europe in early January, after Russia cut off supplies to Ukraine after months of failing to reach a 2009 contract agreement with the Yushchenko- Tymoshenko government. (dpa)