Russian Prime Minister Vladimir Putin has signed a series of key energy deals with Venezuelan President Hugo Chavez during a visit to the capital, Caracas.
Mr Chavez said Russia had agreed to help Venezuela with a nuclear power plant and on building a space industry.
However, the Venezuelan leader, a long-time adversary of Washington, insisted that "we are not building an alliance against the United States".
Bolivian President Evo Morales was also invited to meet Mr Putin in Caracas.
Mr Putin is perhaps Venezuela's most important visitor since US President Bill Clinton in 1999.
The Russian leader gave Mr Chavez a multi-million-dollar down payment for oil exploration rights in the Orinoco River Belt.
Mr Chavez added: "Russia offers help so that Venezuela can have its own industry for the use of outer space.
"We could install a satellite launcher here and a factory. We are already doing so with China, but Russia is offering to support Venezuela build its own [space] industry."
In a televised speech ahead of Mr Putin's arrival, Mr Chavez said: "This is a truly important day for the country and for Latin America. It is a visit of great importance. We are forging, like steel, a new multi-polar world."
At a joint news conference after their meeting, the Venezuelan leader said: "We are prepared to begin drawing up the first project for a nuclear power generator, obviously for peaceful purposes.
"We aren't going to make an atomic bomb," he added.
Venezuela has recently suffered widespread power cuts and is looking to nuclear power as a solution.
US state department spokesman P J Crowley said that "to the extent that Venezuela is going to expend resources on behalf of its people, perhaps the focus should be more terrestrial than extraterrestrial".
The US has expressed concern at Venezuela's purchase of weapons from Russia. However, no new deals have yet been announced.
Mr Chavez insisted: "We are not building an alliance against the United States. We don't care what Washington thinks."
Mr Morales was expected to seek Russian loans to purchase military hardware and to discuss gas and oil exploration in Bolivia.