"The world is global by nature. Mistakes made by individual countries ... will affect the economy at large," he said.
"No matter how big the American market and no matter how strong the American financial system, they are incapable of substituting for global commodity and financial markets," he said.
The Russian president said that Russia's foreign investment strategy was not based on imperialist ambitions, as he detailed ambitious economic goals set out by Vladimir Putin, former Russian president who is now prime minister.
"Russia is a global player and understands its responsibility for the fate of the world," he said.
"We want to participate in setting out the new rules of the game, not out of imperial ambitions ... but because of our energy resources."
Alexander Nekrassov, a former Kremlin adviser, told Al Jazeera that it was an important speech for Medvedev, because "he is basically by himself now without Mr Putin by his side".
"We're listening to his economic programme and how he sees the the future and development of Russia.
"He says it's strong now, and should be treated as an equal economic power in the world, and that we're open for business."
Some analysts regard Medvedev as an economic liberal and since coming to power last month he has launched a number of initiatives aimed at boosting the rule of law, cutting corruption and easing conditions for small businesses in Russia.
Russia's economy expanded steadily under Putin on the back of soaring energy export revenues, with GDP growth at 8.1 per cent in 2007.
|"We want to participate in setting out the new rules of the game, not out of imperial ambitions ... but because of our energy resources"|
Dmitry Medvedev, Russian president
But the economy has recently shown signs of overheating and there is growing concern about risks for foreign investors.
"Russia's economy has to be diversifed," Nekrassov said.
"We have the situation where there are two leaders. The reason Mr Putin stayed away from this economic forum is because we are witnessing a campaign by the Kremlin, which says 'Yes, Mr Medvedev has the power, he is the president'.
"Many people will be thinking a lot of power is still with the prime minister, maybe more than ever before, so this creates confusion for Russians and foreign investors and governments."
"This particular crisis will need to be solved by both of them."
The world's largest energy power has been cushioned from the global credit crisis by high oil prices, and the forum in St Petersburg showcased Russia as a relatively stable economic player.
A key issue on the sidelines of the forum will be the future of
TNK-BP, a Russian-British oil company which is riven by infighting between BP and its Russian partners while facing tax investigations by the Russian authorities.
"The resolution of this dispute ... will send a very strong signal, positive or negative, about the environment for investment in Russia," Andrew Somers, head of the American Chamber of Commerce in Moscow, said at the forum.
Robert Dudley, the chief executive of TNK-BP, was due to address the forum on Sunday as part of a line-up of energy leaders, including the heads of BP, Chevron, ConocoPhillips, ExxonMobil, Shell and Russian gas giant Gazprom.
Officials said contracts worth more than $12bn would be signed at the meeting, where the new St Petersburg Commodity Exchange, due to start trading oil later this year, will also be showcased.