Ukraine revoked the oil and gas license of U.S. company Vanco International, a subsidiary of the Vanco Energy Company, on April 25.
Ukrainian Prime Minister Tymoshenko earlier called for an international investigation into the license, describing the Vanco deal as "plundering of Ukraine's mineral reserves" and accused President Viktor Yushchenko of lobbying for the U.S. firm.
Vanco International signed a 30-year production sharing agreement with former premier Viktor Yanukovych's government in October 2007, covering the Prykerchenska area just south of the Crimean Peninsula.
Under the deal, the company received a 65% stake and Ukraine 35% at the prospecting and development stage. The sides were to go 50-50 with the launch of commercial production.
Vanco Energy Company is an integrated independent oil and gas company which operates its exploration and production activities through its wholly owned overseas subsidiary and subsidiaries of Vanco International Ltd.
The company holds and operates six large licenses in five countries, including the Ivory Coast and Ghana.