By Saikat Chatterjee and Elizabeth Howcroft LONDON (Reuters) -European stocks and Wall Street futures edged slightly higher on Tuesday, but markets remained volatile as the prospect of a ban on Russian oil imports pushed oil prices higher and added to investor fears over inflation. Since the conflict in Ukraine began on Feb. 24, Western sanctions have cut off Russia from international trade and financial markets. U.S. President Joe Biden’s administration is willing to move ahead with a U.S. ban on Russian oil imports even if European allies do not, U.S. sources indicated. Russia warned that pr…