Egyptian mobile operator Orascom Telecom Holding said on Tuesday Algerian authorities had given its local unit Djezzy a final $230 million tax request for the years 2008 and 2009.

The firm said in a statement it had already paid taxes for those years and would take legal steps to challenge the "completely unfounded" reassessment.

Djezzy, Orascom's single biggest revenue earner, has been at the centre of a long-running dispute with Algiers since it was hit with over $600 million in previous back-tax claims and penalties last year.

Uncertainty over the fate of the unit, which Algeria has said it wants to nationalise, has complicated a $6.6 billion deal to sell a majority stake in Orascom and other assets to Russian operator Vimpelcom. 

Orascom said in September it had received preliminary notification of the $230 million reassessment, but that it was not final.

"Without prejudice to their rights under the investment agreement, applicable bilateral investment treaty and applicable laws, OTH (Orascom Telecom Holding) and OTA (Orascom Telecom Algeria) intend to take all necessary legal steps to challenge this completely unfounded reassessment," Orascom said.