Russian president Vladimir Putin has signed agreements on nuclear energy generation with Argentina as part of a Latin American tour aimed at building Moscow's influence in the region.
Argentina has been building nuclear-powered electricity plants to revive its nuclear programme and reduce its dependence on fossil fuels amid an energy crunch. Mr Putin and president Cristina Fernandez said the Russian atomic energy corporation, Rosatom, would be involved with the construction of units in Argentina's Atucha III nuclear power plant.
"These are very important agreements," said Ms Fernandez, who had been out of the public eye for a week due to a throat infection.
"Argentina is a leader in Latin America in terms of nuclear energy generation," she said at a joint news conference at the presidential palace. "They reaffirm our bonds of friendship and strategic links."
Argentina has one of the world's largest deposits of shale oil and gas, but only a few companies have made commitments to develop the fields as many fear the government's interventionist energy policies.
Although a deal on the shale deposits was not announced, Ms Fernandez said members of the Russian delegation travelling with Mr Putin will visit Argentina's Vaca Muerta (Dead Cow) deposit in Neuquen province.
"We're talking about Russia - one of the world's top producers of gas and oil in the world. But we Argentines also have our own and it seems like others have noticed," Ms Fernandez said.
The Russian leader will later arrive in Brazil for a summit of leaders from the BRICS nations: Brazil, Russia, India, China and South Africa.
"Argentina is one of Russia's top strategic partners in Latin America. We co-operate in vast sectors and I'm in constant contact with the president," Mr Putin said. "We also have similar positions in the international arena."
About 150 members of the local Ukranian community waved flags and held large banners outside the Pink House presidential palace to protest against Russia's annexation of Crimea and alleged support for separatists elsewhere in Ukraine.
A few dozen activists also turned out to protest over anti-gay laws and prejudice in Russia, which does not recognise gay marriages or civil unions. Mr Putin approved a law last year banning what it calls gay "propaganda" from reaching minors.
Argentina is the first country in Latin America to legalise gay marriage. Two Russian homosexuals married in Argentina earlier this year and are also seeking asylum.
Earlier, Mr Putin stopped in Cuba, a key Soviet ally during the Cold War which is backing Moscow in its dispute with the West over Ukraine.
The two countries signed about a dozen accords in areas such as energy, industry, health and disaster prevention.
Russian companies will participate in petroleum projects around Boca de Jaruco on the island's north coast, and that co-operation will extend to offshore oil deposits, Cuban government website Cubadebate said.
Another agreement covered infrastructure at a new port project that Cuba hopes will become a regional shipping centre and attract much-needed foreign investment.
"We are talking about the possibility of creating in Cuba a grand transportation hub with a possible modernisation of the maritime port of Mariel and the construction of a modern airport with its respective cargo terminal," Mr Putin said.
Moscow is also forgiving 90% of Cuba's Soviet-era debt, which totals more than 35 billion US dollars (£20.5 billion). The remainder will be invested in education on the island, Mr Putin added.