President Barack Obama on Wednesday evening formally announced new sanctions on Russia during a statement from the White House.

The Obama administration leveled its most punitive sanctions yet against Russia and the government of President Vladimir Putin on Wednesday, amid increasing tensions on the Ukrainian border between Ukraine's forces and pro-Russian separatists.

"These sanctions are significant, but they are also targeted," Obama said, adding the steps were taken with an emphasis on limiting the potential "spillover" for U.S. companies.

The new sanctions are aimed at a series of large banks and energy and defense firms, marking a significant escalation in the U.S.'s standoff with Russia. Up to this point, the sanctions had only been aimed at several Russian individuals and their businesses involved in the destabilization of the situation in Ukraine.

Among the targeted firms on the new sanctions list include Rosneft, the world's largest oil company; Gazprombank, Russia's largest private bank; Novatek, Russia's largest independent natural-gas producer; and Vnesheconombank, a development lender.

Other entities were included on the list, including the entirety of the self-proclaimed "Donetsk People's Republic" and "Luhansk People's Republic" in Ukraine. Several Russian government individuals were also sanctioned, including senior Russian Federal Security Service official Sergey Beseda.

The sanctions restrict Russian access to U.S. debt markets. Senior administration officials portrayed the entities sanctioned as now being cut off "from the U.S. financial system and the U.S. economy."

Obama's announcement of the new sanctions came after he addressed a laundry list of current crises around the world — the disputed elections in Afghanistan, the negotiations on Iran's nuclear program, and the Israeli-Palestinian crisis.

"We live in a complex world and a challenging time," he said.