The White House said Obama spoke with Merkel about the concerning situation in eastern Ukraine, where pro-Russian separatists, apparently with support from Moscow, continue an orchestrated campaign of incitement and sabotage to undermine and destabilise the Ukrainian state.
"The leaders again called for Russia to move its troops back from the border region. They also discussed issues relating to the forthcoming meeting of the Ukrainian, Russian, and the US foreign ministers and EU High Representative," the White House said.
"The President underscored the need for the United States, European Union, and other global partners to be prepared to meet further Russian escalation with additional sanctions," it said.
Earlier, US Treasury Secretary Jacob Lew, met Russian Finance Minister Anton Siluanov, on the sidelines of the World Bank-International Monetary Fund Spring Meetings, during which he emphasised that Russia's ongoing occupation and purported annexation of Crimea is illegal and illegitimate.
Lew told his Russian counterpart that in addition to the sanctions already imposed in response to Russia's occupation and purported annexation of Crimea, the US is prepared to impose additional significant sanctions on Russia if it continues to escalate the situation in Ukraine.