Shares in the tiny British oil company have soared since it announced a deal in war-torn Sudan. But a consortium fronted by French group Total has claimed that it has rights over the area.

Costello Garang Ring Lual, a member of the national executive committee of Sudan's People's Liberation Movement and south Sudan's international development commissioner, told the Guardian: "It is not possible for Total to come back.

"We have controlled this area for the last 20 years, we have fought for it. For someone to think they can come in and take it is just wrong. The government in the north [Khartoum] knows we are right. The agreement is very clear."

Total claims a production-sharing contract struck in 1980 and re-signed in December, is still valid. The deal covers a huge area of south Sudan, including Block Ba - 67,500 sq km of land that some observers believe could contain 5bn barrels of oil.

Mr Garang's comments come as Mr Edmonds puts the finishing touches to a deal that will see the SPLM sell 60% of Block Ba in return for a 50% holding in his company, White Nile. The deal is expected to be announced next week, at which point White Nile shares will start trading again.

They were suspended just over a month ago after they had risen 13-fold in less than a week, a performance that revived memories of the dotcom boom.

At the suspension price of 137p a share, White Nile was valued at £190m despite the fact that its only tangible asset was the £9m of cash it raised in a private placing at 10p.

Mr Garang also sought to clarify recent reports that the oil ministry in Khartoum has control over oil deals in the south.

He said that Block Ba belonged to the people of the south and that the peace agreement, which brought to an end 21 years of civil war, specified that all contracts signed before January 9 would be honoured. White Nile's agreement with the SPLM pre-dates Total's renewed claim on Block Ba by several months.

He also pointed out that Sudan's new petroleum commission, which will have to approve the White Nile transaction once it is up and running, will include both government and SPLM members.

Asked why the SPLM had teamed up with a former test cricketer rather than a multi-national oil company to develop the oilfield, he said that the deal would help the new regional government pay for several big infrastructure projects, including railway lines to Kenya and Uganda and a telecoms network.