MOSCOW, Aug. 12 - Russia believes that the 3+1 format cannot be applied to cooperation between the Customs Union and Ukraine.

A Kremlin source told the press on Friday that at a Thursday meeting of Russian President Dmitry Medvedev and Ukrainian President Viktor Yanukovych, the Russian side "gave explanations concerning the possible parameters of cooperation between Ukraine and the Customs Union."

"Such cooperation can be conducted on the basis of Ukraine's full-scale membership in the Customs Union," the source said.

"The 3+1 format is unacceptable for these purposes," the source said.