KIEV, Nov. 13 - Ukraine should increase by 25% the tariff it charges Russia for shipping natural gas to the European Union in response to an expected hike in gas prices, a former top energy advisor to President Viktor Yushchenko said.

Oleksiy Ivchenko, who as the chairman of Naftogaz Ukrayiny had engineered a key natural gas agreement with Russia in early 2006, said he met Yushchenko recently to suggest an “adequate” response with the tariff hike.