Russia, Belarus, and Kazakhstan have failed to reach agreement on establishing a joint customs union.
In a statement from St. Petersburg, where leaders were discussing the possible union, Russian Prime Minister Vladimir Putin said the sides "couldn't agree on all the issues."
He said duties within the auto and aviation industries were stumbling blocks in the talks, but that negotiations will continue.
Putin's Belarusian counterpart, Sergei Sidorsky, suggested that oil duties were the major sticking point.
Earlier this year, the three countries agreed to establish the union to boost trade and investment.