Police in the Ukrainian city of Odessa said 38 people died as the result of a building fire that broke out during a clash between pre-Russian rioters and pro-government crowds, according to the Associated Press.

The violence worsened throughout the evening in Odessa. On a livestream, crowds described by reporters on the ground as pro-Russian threw Molotov cocktails from the roof of a building. Pro-Ukrainians stormed the building, which is now ablaze, and machine gun fire could be heard. Some of those trapped by the fire reportedly jumped out of the burning building. After the clash finished people began laying flags over the dead bodies in the street outside of the building.

Pravy Sektor (Right Sector), a pro-government paramilitary collective in Ukraine, published an announcement on its Facebook page earlier on Friday on the situation in Odessa, saying it had mobilized a group that “will harshly cut off any destabilising action with all available means and methods.” 

U.S. President Barack Obama and German Chancellor Angela Merkel said on Friday that harsher sanctions on Russia were possible if it interferes in Ukraine's May 25 elections.

After a meeting at the White House, both leaders reaffirmed their countries' commitment to working with the other to pressure Russia through sanctions to stop meddling in eastern and southern Ukraine and release journalists and observers from the Organization for Security and Co-operation in Europe, who are being held hostage. If Russia does not comply, Merkel said harsher sanctions would be “unavoidable.”

Both Obama and Merkel said they wanted to see a diplomatic resolution to the situation in Ukraine, but would have no option other than to move forward with harsher sanctions if Russia did not exercise restraint. The next round of sanctions, Obama said, would target certain sectors of the Russian economy and would “include greater costs,” affecting investment in the country.

But Obama said the sanctions would most likely not hit the oil sector.

“The idea that you are going to turn off the tap … I think is unrealistic,” he said.  “But there are a range of approaches that can be taken not only in the energy sector but in the arms sector.”

As Obama and Merkel were holding their press conference, the U.N. Security Council met in New York to discuss the escalating violence in Ukraine, where clashes have turned deadly in the southern port of Odessa.

U.S. Ambassador to the United Nations Samantha Power said her country was "outraged" at Russia’s intervention in Ukraine and its unwillingness to comply with international law. Powers said though Russia can exercise its veto in the security council, “it cannot veto the truth.”