The United States announced financial sanctions Monday against rebel territories in eastern Ukraine freshly recognized by Russia and warned that more were ready if necessary.

President Joe Biden will issue an executive order to “prohibit new investment, trade, and financing by US persons to, from, or in the so-called DNR and LNR regions of Ukraine,” White House Press Secretary Jen Psaki said, referring to the breakaway regions of Donetsk and Lugansk.

The order will “provide authority to impose sanctions on any person determined to operate in those areas of Ukraine,” Psaki said, adding that the measures are separate from wider Western sanctions ready to go “should Russia further invade Ukraine.”

The two self-proclaimed republics already have extremely limited dealings with US citizens. However, the sanctions herald a new phase in what could soon become the most dangerous East-West confrontation since the collapse of the Soviet Union.

US Secretary of State Antony Blinken slammed Russia’s recognition of the separatist regions as a sign President Vladimir Putin had no interest in diplomacy.

Blinken said in a statement that recognizing the territories’ independence “directly contradicts Russia’s claimed commitment to diplomacy, and is a clear attack on Ukraine’s sovereignty.”

“Russia’s decision is yet another example of President Putin’s flagrant disrespect for international law and norms,” he said, adding in a separate tweet that the United States “will take appropriate steps in coordination with partners.”

Biden has led a coalition of European and other US allies to craft a package of what they say will be crippling economic sanctions on Russia should troops massing on Ukraine’s borders start an attack.

While the Kremlin has for weeks denied invasion plans, it has at the same time built up an enormous force of troops and heavy weaponry on three sides of Ukraine.

Shortly after recognizing their independence, Putin ordered troops into the two breakwaway regions as part of a “peacekeeping” operation.

Moscow provided no details or date for any deployment, with the order saying only that it “comes into force from the day it was signed”.

On Friday, the deputy US national security advisor for international economics, Daleep Singh, warned that sanctions would turn Russia into an international “pariah.”

Moscow has for years been giving the separatist rebels covert financial, political and military backing.

The White House said that after Putin recognized the regions as independent, Biden talked by phone with Ukrainian President Volodymyr Zelensky for 35 minutes to “reaffirm” the US commitment to Ukrainian sovereignty. He also detailed the plan for sanctions on Russia.

Biden later spoke for half an hour with two key European allies — French President Emmanuel Macron and German Chancellor Olaf Scholz, an official said. The three leaders “strongly condemned” Putin’s decision and discussed how to coordinate their response.

The White House did not respond immediately to questions about whether there was still any consideration being given to a suggested summit between Biden and Putin.