I.Coast says Ghana's oil activity in disputed zone threatens interests

* Two countries in dispute over oil-rich border area

* Oral arguments opened on Sunday at international tribunal

* Ivory Coast wants exploration stopped pending boundary decision

By Joe Bavier

ABIDJAN, March 29 (Reuters) - Ivory Coast argued in an international tribunal on Sunday that allowing Ghana to continue oil exploration in a disputed offshore area pending a ruling on their border line would do irreparable damage to its economy and energy policy.

The two West African neighbours have asked the International Tribunal of the Law of the Sea (ITLOS) in Hamburg to rule on the location of their shared maritime boundary.

London-listed Tullow Oil (LSE: TLW.L - news) is due to finish work on its TEN project in the disputed zone and start pumping oil by mid-2016.

Ivory Coast has submitted a request to ITLOS for a suspension of Ghana's ongoing exploration activities in the zone pending a final ruling, which could take three years.

A decision on Ivory Coast's request is expected next month.

In its first round of oral arguments, Ivory Coast said Ghana was accelerating development in the zone, which would leave it to face a fait accompli.

Michael Wood, a special adviser to the Ivorian delegation, said that not granting the suspension "could irreparably compromise Cote d'Ivoire's entitlement to formulate and pursue a national policy with respect to the use of natural resources".

Paul Reichler, a member of Ghana's legal team, said that Ivory Coast had for at least the last 40 years accepted the demarcation that Accra considers to be the boundary between the two nations.

"There was an agreed border separating their respective maritime territories, and it consisted of an equidistant line whose specific coordinates were identified and were reflected in their oil concession agreements," he said.

The argument was rejected at the tribunal by Ibrahima Diaby, director-general of hydrocarbons for Ivory Coast's energy ministry.

"I regret that Ghana should rewrite our shared history by asserting that Cote d'Ivoire expressly accepted as a maritime boundary between the two states the line along which oil blocks were granted by the two states," he said.

Ghana is seeking a dismissal of Ivory Coast's request for a provisional suspension.

Ghana downplayed fears of a possible suspension of the TEN project earlier this month after Ivory Coast introduced its request, saying a ruling in favour of the Ivorian government was "highly unlikely".

But Tullow lost over 200 million pounds ($308 million) of its market value on March 2 over concerns that the boundary dispute could delay its TEN project. (editing by Jane Baird)