Obama tells 'defiant' Putin to withdraw forces from Ukraine

President Barack Obama has told his Russian counterpart President Vladimir Putin that his country sending troops into Ukraine is a 'clear violation' of that country's sovereignty.

According to the White House, Obama made the comments in a 90-minute phone call with Putin on Saturday, expressing 'deep concern' over Russia's actions in the past two days.

Obama also called on Putin to de-escalate tensions by withdrawing his forces back to bases in Crimea and to refrain from any interference elsewhere in Ukraine, Fox News reports.

However, a defiant-sounding statement issued later by the Kremlin in Moscow said Putin stressed to Obama that the situation in Ukraine posed a 'real threats' to the life and health of Russian citizens, the report said.

Obama also said Russia's actions were a 'violation of international law,' which would lead to 'greater political and economic isolation,' the report added.