President Obama on Wednesday assured Ukrainian Prime Minister Arseniy Yatsenyuk that the international community would “completely reject” a Russian-backed referendum on Crimean secession.

Obama hosted Yatsenyuk at the White House as Crimea, which was seized by Russian military forces, prepares to hold a referendum on Sunday to leave Ukraine and join Russia.

The president called the planned referendum a “slapdash election” and vowed that if it went ahead the international community would be “forced to apply a cost to Russia’s violation of international law.”

“There’s another path available and we hope President Putin is willing to seize that path,” Obama continued. “But if he does not, I’m very confident that the international community will stand firmly behind the Ukrainian government.”

Obama suggested that Ukraine was willing to discuss the status of Crimea, but that was not “something that can be done with the barrel of a gun pointed at you.”

Russia's military incursion came after Moscow-backed former Ukrainian President Viktor Yanukovych was removed from power after months of protests.

Russian President Vladimir Putin has said that the rights of the majority ethnic-Russian population in Crimea were being threatened by Ukraine's new interim government, and has allowed plans for the referendum to go ahead.

The U.S. has called on Russia to return military troops to their bases, initiate talks with the government in Kiev, allow international monitors in Crimea and call off the referendum.

Russia, though, has refused to back down and the White House has characterized the crisis as a power grab by Moscow to retain influence in Ukraine.

Obama dismissed as a “zero-sum formulation” the idea that Ukraine had to choose between Russia and the West.

Secretary of State John Kerry is slated to meet with Russian Foreign Minister Sergey Lavrov in London on Friday.

Obama said the U.S. will “keep on pressing” Russia to de-escalate the situation.

Yatsenyuk said that the Ukrainian people would “never surrender” in their fight for sovereignty.

“My country feels that the United States stands by the Ukrainian people,” he said.