Russia, Belarus and Kazakhstan have agreed to set up a Eurasian economic union, modelled on the EU, with a target date of 2015.
The three countries already have a customs union but now aim to go further by removing trade barriers.
Their respective presidents signed a deal to create an executive body similar to the European Commission.
Earlier this year, Russian Prime Minister Vladimir Putin denied the bloc would re-create the Soviet Union.
In a ceremony broadcast live on Russian television, President Dmitry Medvedev said that "without doubt this will be decisive in the future of our countries". He added that the prospect of a Eurasian union had also aroused interest from several other states.
Kyrgyzstan and Tajikistan in particular are said to be looking at the project.
Mr Medvedev also did not rule out the possibility that the union would take shape even earlier than 2015: "If the prerequisites are there, we shall move faster, if we are able to."
Although Russia is spear-heading the plan, Mr Medvedev praised the Kazakh leader, Nursultan Nazarbayev, as its creator as far back as the 1990s "when the very word integration was regarded as a remnant of Soviet-style vocabulary".
In a newspaper article last month, Vladimir Putin insisted that there was no talk of reforming the USSR, arguing that it would be naive to copy what had been abandoned in the past.
Under the customs union that came into operation in July 2010, Belarus, Russia and Kazakhstan agreed to remove tariffs and customs controls along their shared borders. They will then form a single economic space at the start of 2012.
Mr Nazarbayev said they would also have to come to a deal on inflation and debt levels before economic union could begin.
All three countries are still members of the Commonwealth of Independent States, along with eight other nations, including Ukraine.