In a phone call on Saturday, Hollande and Obama insisted on the "need for Russia to withdraw forces sent to Crimea since the end of February and to do everything to allow the deployment of international observers," it said.
"If there's a lack progress in this direction, new measures will be taken which would noticeably affect relations between the international community and Russia, which is in no-one's interest," it said.
The months-long crisis in Ukraine, which resulted in the ouster last month of pro-Russian president Viktor Yanukovych, has worsened since the Crimean parliament's decision to secede from Ukraine and stage a referendum on joining Russia.
Ukraine also said there were now 30,000 Russian soldiers in Crimea -- 5,000 more than the contingent allowed under an existing agreement with Kiev.
Russia says it has stepped up protection of its naval base in Crimea and is working together with local self-defence units but refuses to acknowledge deploying extra troops.
"In the current grave circumstances," Hollande and Obama "stressed the importance for Russia to agree rapidly to the formation of a contact group allowing for Ukraine and Russia to engage in dialogue, with a view to favouring a peaceful exit to the crisis and restoring fully Ukraine's sovereignty and territorial integrity," the statement said.
"They recalled the absence of any legal basis to the planned referendum in Crimea on ," the presidency said.
The two leaders also agreed, the statement added, to continue their support for the new pro-western authorities in Ukraine as well as for the preparation for presidential elections on , "under international control and in the greatest transparency".
The United States has already imposed visa bans and set the stage for wider sanctions against Russia over the seizure of the Ukrainian region of Crimea by pro-Russia forces.