(Adds detail, analyst, graphic)
By Manuel Mucari
MAPUTO Aug 29 (Reuters) - Sales by foreign companies of assets in Mozambique will be taxed at a fixed rate of 32 percent from next year, a tax official said, as the government tries to extract more benefits from its huge gas discoveries.
Civil society groups and the opposition have criticised big tax breaks that were granted to foreign firms as the southern African nation struggled to attract investment in the years following a bloody civil war which ended in 1992.
Mozambique is now a key prospect for the export of liquefied natural gas because of the size of recent discoveries, its location en route to Asia and its appeal to buyers trying to diversify away from big suppliers Qatar and Australia.
Up to now, the sale of local assets belonging to foreign companies in Mozambique had been taxed on a progressively declining basis, depending on the length of time they were held.
This is why Cove Energy paid a rate of only 12.8 percent when it sold out to Thailand's PTT Exploration and Production in 2012.
Mozambique's parliament passed an amendment to the tax regime last year, stipulating that sales of assets held by non-resident firms would be taxed at 32 percent without consideration for the period they were held.
But the new law was put on hold, pending a review by the president of the southeast African state.
"The constitutional issues that delayed the passing of the tax law have been overcome and the president has promulgated the law," Rosario Fernandes, head of the tax authority, told Reuters late on Wednesday.
"Come Jan. 1, capital gains in all mega-projects, including oil and gas, will be taxed according to the new legislation."
The fixed-rate tax will affect any future gas field deals in Mozambique's attractive Rovuma basin and could spur companies with agreements on the table to try get them wrapped up by the end of the year.
Italian oil and gas company Eni agreed this month to pay the former Portuguese colony $400 million in taxes on its $4.2 billion sale of a gas field stake to China's CNPC.
Eni also pledged to build a power plant, which Fernandes said is worth another $130 million.
If the new tax rule had been applied, Eni's tax bill on the deal would have been as high as $1.35 billion, analysts said.
They said Mozambique was receptive to approving the Eni deal under the existing, more flexible tax rule given Eni's financial strength and ability to get capital-intensive LNG plants off the ground. The government also has a close relationship with China, which has invested a lot in infrastructure in Mozambique.
India's Oil and Natural Gas Corp (ONGC) said this week it had agreed to buy 10 percent of a gas block from Anadarko Petroleum Corp for $2.64 billion.
"Anadarko is relatively well-placed to negotiate an approval before year-end 2013, thereby securing a lower tax bill," Mark Rosenberg, an analyst at Eurasia Group, said in a note.
"Like Eni, Anadarko is critical to developing the Mozambican gas industry: it is the lead operator of the Area 1 block and is jointly leading construction of a large LNG plant at Palma with Eni," Rosenberg added. "Still, a pre-2014 approval is far from certain."
Approval on other outstanding deals may also slip into 2014.
In June, ONGC and state-run Oil India Ltd agreed to buy a 10 percent stake in a gas field from Videocon Group for $2.48 billion, while Norway's Statoil is selling 25 percent of its licence to Japan's INPEX.
Mozambique has become an attractive gas investment destination, with current estimates for its reserves at 150 trillion cubic feet - enough to supply Germany, Britain, France and Italy for 15 years - but sporadic raids by former rebels this year have raised fears the country could slip back into conflict.
In neighbouring Tanzania, which also boasts attractive gas discoveries, albeit of smaller size, capital gains are taxed at a rate of 10 and 20 percent for residents and foreign shareholders, respectively.
(Additional reporting by Fumbuka Ng'wanakilala in Dar es Salaam; writing by Agnieszka Flak; editing by Pascal Fletcher and Tom Pfeiffer)