A leader of the Russian-controlled separatists in eastern Ukraine is calling on Russian President Vladimir Putin to recognize the separatist regions as independent of Ukraine, Russian media is reporting.

Denis Pushilin, the leader of the self-proclaimed People’s Republic of Donetsk, is also asking Putin to consider making a treaty on mutual military defense.

Recognition would open a path to Russia potentially annexing the regions and possibly openly sending troops there.

The Russian parliament last week voted to appeal to Putin to recognize the two separatist self-proclaimed republics, though Putin initially signaled he wouldn’t do so immediately.

The self-proclaimed People’s Republics of Donetsk and Lugansk, the two unrecognized state-lets in Ukraine’s eastern Donbas region, were formed after Russia stoked conflict in the Russian-speaking region of Donbas in 2014.

In the last week Russia and the separatist regions have dramatically escalated tensions, accusing Ukraine of an imminent attack and building a pretext for Russian intervention.

Russia’s senate is due to hold a session on Tuesday to discuss the situation in Ukraine and there's speculation the senate might address the issue of recognition.

-ABC News' Patrick Reevell

National security adviser Jake Sullivan told ABC News' "Good Morning America" Monday that President Joe Biden is prepared in principle to meet Russian President Vladimir Putin if there is no invasion, but that unfortunately, an invasion still seems likely.

"President Biden made clear all along he's prepared either way. He's prepared to engage in high level diplomacy to resolve this peacefully and he's equally prepared to rally our allies and partners to impose costs and consequences on Russia should they choose to invade," Sullivan said.

"He indicated to the French president yesterday in principle he would be prepared to meet with Putin if President Putin stood down from his invasion," Sullivan said. "We can't say anything other than indications on the ground look like Russia is still moving forward."

Sullivan indicated the window for diplomacy will remain open until more significant military action is seen, but that the window gets smaller as time goes on.

"We never give up hope on diplomacy until the missiles fly or the tanks roll," Sullivan said. "We've been working hard for months with our allies and partners to get Russia to sit down in a serious way at the table, even as recently as yesterday the president indicated his readiness to do that. Russia has not shown the same kind of willingness on their side. The likelihood there's a diplomatic solution given the troop movements of the Russians is diminishing hour by hour."

Asked if sanctions will be enough to stop Russia without sending U.S. forces to Ukraine, Sullivan said the U.S. is determined to impose sanctions in the long-term to strangle Russia's ambitions without the use of ground forces.

-ABC News' Sarah Kolinovsky

The Kremlin has said it is still “premature” to talk about a summit between President Joe Biden and President Vladimir Putin, though it didn’t rule out that one could take place.

White House press secretary Jen Psaki on Sunday said Biden and Putin have agreed “in principle” to meet, provided Russia did not invade Ukraine.

French President Emmanuel Macron announced the possibility of a meeting after speaking with both leaders on Sunday, amid intense diplomatic efforts to try to dissuade Putin from launching an invasion the U.S. fears could come this week.

Kremlin spokesman Dmitry Peskov said that for now there’s only an agreement for Russia and the U.S. to speak at a lower level, between U.S. Secretary of State Antony Blinken and Sergei Lavrov, the Russian foreign minister. That meeting is scheduled for this week.

Peskov seemed to suggest that an agreement on a meeting between Biden and Putin would depend on the outcome of those talks.

“I can say that an understanding has been reached that we need to continue the dialogue at the level of ministers," Peskov told reporters on Monday. "But to talk about some kind of concrete plans about organizing any summits is for now premature.”

Contacts between Biden and Putin can be arranged quickly, if necessary, he said.

-ABC News' Patrick Reevell

The United States has obtained information of potential Russian operations against Ukrainian targets as part of a potential invasion, including targeted killings, kidnappings, detentions and torture, the U.S. alleged in a letter to the United Nations obtained by ABC News.

“We have credible information that indicates Russian forces are creating lists of identified Ukrainians to be killed or sent to camps following a military occupation,” U.S. Ambassador Bathsheba Nell Crocker wrote to Michelle Bachelet, the U.N. high commissioner for human rights.

That includes the “likely use” of lethal measures to “disperse peaceful protesters or otherwise counter peaceful exercises of perceived resistance from civilian populations,” Crocker wrote.

Secretary of State Antony Blinken alluded to this during his remarks to the U.N. Security Council on Thursday, telling his fellow diplomats, “Conventional attacks are not all that Russia plans to inflict upon the people of Ukraine. We have information that indicates Russia will target specific groups of Ukrainians.”

In addition, sources told ABC News last Tuesday that the U.S. believed Russia aimed to move into Kyiv to decapitate the Ukrainian government and install their own.

But this new letter goes further, saying Russia “would likely target those who opposes Russian actions, including Russian and Belarusian dissidents in exile in Ukraine, journalists and anti-corruption activists, and vulnerable populations such as religious and ethnic minorities and LGBTQI+ persons.”

Ambassador Michele Sison, the top U.S. diplomat for international organizations, is headed to Geneva this week to meet Bachelet at the U.N. headquarters there, the State Department announced Sunday.

“The United States is gravely concerned that a further Russian invasion of Ukraine would produce widespread human suffering. In light of OHCHR’s important mandate and its reporting presence in Ukraine, we wish to share this information with you as an early warning that a further Russian invasion of Ukraine may create a human rights catastrophe,” Crocker added in the letter.

-ABC News’ Conor Finnegan