"We will continue to take the approach that we have taken in the past, which is to ratchet up the pressure on Russia," Obama told a news conference in New Delhi.
"And I will look at all additional options that are available to us, short of military confrontation, and try to address this issue."
Fighting has flared in Ukraine in recent days after the rebels ruled out more peace talks.
On Saturday, 30 civilians were killed after rebels launched an offensive against the strategic port of Mariupol.
Russia, which the West accuses of supporting the separatists, prevented the U.N. Security Council on Saturday from criticizing rebel statements and condemning the upsurge in violence.
Moscow continually denies sending forces and weapons to eastern Ukraine, despite what Kiev and the West say is irrefutable proof.
More than 5,100 people have been killed since the conflict erupted in April last year.
"We are deeply concerned about the latest break in the ceasefire and the aggression that these separatists - with Russian backing, Russian equipment, Russian financing, Russian training and Russian troops - are conducting," Obama said.
"I have been very clear that it would not be effective for us to engage in a military conflict with Russia on this issue. But what we can do is continue to support Ukraine’s ability to control its own territory."
He said this has involved a combination of economic pressure on Russia through sanctions, providing Ukraine with the support it needs to sustain its economy, helping its military with basic supplies and equipment, and training and exercises with NATO.
Source: Google News