Irish oil and gas explorer Aminex Plc said on Friday it would increase its stake in a natural gas-bearing exploration block in Tanzania through an agreement with Australia's Key Petroleum.

Aminex said it would raise its stake to 65 percent from 50 percent in the Nyuni Production Sharing Agreement. The agreement covers the Kiliwani North field, which is estimated to hold 45 billion cubic feet of gas.

Aminex said it would fund a 20 percent share in the initial cost of the forthcoming Nyuni-2 exploration well in return for a 15 percent interest. Aminex, through its local subsidiary Ndovu Resources, is also Nyuni's operator.

Nyuni-2 is due to be spudded in April, and a rig contract is in the final stages of negotiations, Aminex said in a statement.

The Key Petroleum share will fall to 5 percent under the terms of the farm-out, which is subject to Tanzanian government approval.

Other firms with shareholding in the Nyuni block are United Arab Emirates' Ras Al Khaimah Gas Company (RAK Gas) with 25 percent and Australian Bounty Oil with 5 percent.

Besides Kiliwani North, other natural gas discoveries include Mnazi Bay in Mtwara in southeast Tanzania, Songo Songo off its eastern coast and Mkuranga near the commercial capital of Dar es Salaam.

Tanzania is already using the gas from Songo Songo to generate electricity and to power industries in Dar es Salaam.

Earlier on Friday, a senior official at state-run Tanzania Petroleum Development Corporation said the country would launch its fourth deep offshore bidding round in April.