The establishment of a free trade area between Ukraine and the European Union will bar Ukraine from joining the Belarusian-Kazakh-Russian Customs Union forever, says Russian presidential advisor Sergei Glazyev.

"A free trade agreement with the European Union would close the opportunity of joining the Customs Union of Russia, Belarus and Kazakhstan forever," Glazyev said on Inter television channel on Friday evening.

Ukraine would gain a lot of advantages if it joins the Customs Union, as appealing markets and resources will be open to it, he said.

Glazyev vowed that the countries making up the Customs Union enjoy absolute equitability in decision-making processes.

However, if Ukraine sets up a free trade area with the EU, the Customs Union members will protect their market from an influx of goods imported from Europe, Glazyev said.