Building on measures unveiled two weeks ago, the US expanded its sanctions to more Russian banks and defence companies, and blocked the exports of specific goods and technology to Russia's energy sector, Xinhua quoted Obama telling reporters at the White House.
He said the US is formally suspending credit that encourages exports to Russia and financing for economic development projects in Russia.
"If Russia continues on this current path, the costs on Russia will continue to grow," Obama added.
The US imposed sanctions against three state-owned Russian banks, namely Bank of Moscow, Russian Agricultural Bank, and VTB Bank OAO, said the US Treasury Department in a statement.
The move prohibits US people from providing new financing to the three financial institutions, limiting their access to the US capital markets.
The Treasury Department also designated and blocked the assets of United Shipbuilding Corporation, a defence technologies firm based in St. Petersburg.
"The major sanctions we're announcing today will continue to ratchet up the pressure on Russia, including the cronies and companies that are supporting Russia's illegal actions in Ukraine," Obama said.
The new punitive measures came after the European Union announced earlier in the day that it has agreed a package of "significant" additional restrictive measures targeting sectorial cooperation and exchanges with Russia.
The US has accused Russia of supporting militants in eastern Ukraine who were allegedly responsible for the downing of a Malaysian jetliner that killed 298 people on board.
On Tuesday, Obama denied that the West is at a new Cold War with Russia, emphasizing that "it is a very specific issue related to Russia's unwillingness to recognize that Ukraine can chart its own path."
While the Russians have said that they want to de-escalate the conflict, their actions have not shown a shred of evidence that they really have "a legitimate desire to end the violence and end the bloodshed", US Secretary of State John Kerry said earlier Tuesday.