In a one-on-one conversation Tuesday, U.S. President Barack Obama personally warned Russian President Vladimir Putin that unless an acceptable peace deal is reached in talks scheduled to be held in Minsk today, Russia will face increased costs for its invasion of Ukraine’s Crimean peninsula and its continued support of separatist rebels in eastern Ukraine.

The conversation took place a day after Obama confirmed that he has asked aides to provide him with options for dealing with the ongoing violence in Ukraine, including the possibility of providing weapons to the Ukrainian military, which is currently battling separatist forces that Western nations believe Russia is supplying with both advanced equipment and soldiers.

Related: If the U.S. Arms Ukraine, Russia Vows Retaliation

While Obama has remained equivocal about whether or not the U.S. would arm Ukraine, members of Congress have been increasingly adamant about the need to provide Ukraine with, at minimum, defensive weaponry.

On Tuesday, the top Republican and top Democrat on the House Armed Services Committee jointly sponsored legislation that would provide the Ukrainian government in Kiev with $1 billion in weapons and other support to fend off “foreign aggressors.”

Rep. Mac Thornberry (R-Texas) and Rep. Adam Smith (D-WA) jointly proposed the measure, which is likely to find substantial support in the House, where members have already voted in favor of providing military assistance to the government in Kiev.

Although he may hesitate to arm Ukraine, Obama is unequivocal about giving any credence to Moscow’s claims that it is not involved in the Ukrainian conflict. In remarks Monday, he said that Russian troops and arms are already in Ukraine and continue to flow there. “These are the facts,” he said.

Related: Obama – If Putin Really Wanted Ukraine, He Could Take It

In negotiations that dragged into early Wednesday morning European time, representatives of Russia, Ukraine, the separatists and European powers struggled to come to terms on a ceasefire that would allow Wednesday’s planned discussion to take place without ongoing bloodshed. Despite multiple reports to the contrary, at well past midnight in the Belarusian capital of Minsk, where the negotiations are taking place, officials said no deal had been reached.

The possibility that the U.S. might provide arms to the Ukrainian army has prompted promises of retaliation from the Russian government. Russian media have, in the past 24 hours, been reporting increasingly aggressive responses from the Kremlin to the possibility that the U.S might give Ukraine military support.

Related: Putin Won’t Commit to Peace Talks on Ukraine

On Monday, an anonymous member of the Russian Defense Ministry’s advisory board promised “asymmetric” responses against U.S interests worldwide.

By Tuesday, Russian officials were no longer demanding anonymity.

“The Americans are trying to draw the Russian Federation into an interstate military conflict, to achieve regime change through the events in Ukraine and to ultimately dismember our country,” said Nikolai Patrushev, who heads the Kremlin’s security council.

Wednesday’s talks in Minsk look increasingly like the last chance to avoid all-out war in Europe for the first time in more than a decade.

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