British oil exploration firm Premier Oil said it has withdrawn from Block L10A, offshore Kenya, after conducting a further exploration review. Premier said in a statement received on Tuesday that it will retain its 25-percent equity in the adjacent Block L10B, where prospect maturation is ongoing and a "drill of drop" decision will be made by mid-2014. "Prospect maturation of this block is ongoing and a 'drill or drop' decision will be made by mid-2014," the company's CEO Simon Lockett said in a statement. "Whilst we remain committed to exploration in Kenya, we continue to focus our resources on projects that meet our internal corporate investment metrics and to high grade our exploration portfolio accordingly," Lockett said. Premier held a 20 percent equity stake in Block L10A. Other partners in Block L10B are BG Group (45 percent, operator), PTTEP (15 percent) and Pancontinental Oil & Gas (15 percent). Kenya has witnessed intensified exploratory activity since 2003, which has also led to the discoveries of oil and gas in Uganda and Tanzania. There is also ongoing exploration in Ethiopia. Exploration experts said the semi-arid regions of northern and north-eastern Kenya, have the curvy rocks, formed millions of years back, when the region was an ocean. East Africa is now regarded as a promising frontier especially following discoveries made by Tullow Oil. Analysts said one of the contributors for slow exploration of minerals in Kenya has been lack of mapping of the resources. The East African Rift Basin system is one of the last of the great rift basins to be explored.