Ukrainian President Volodymyr Zelenskyy said Tuesday he won't introduce martial law for now because his government doesn't believe that Russia will mount a "large-scale" invasion.

"We believe that there won't be a war, a powerful one, against Ukraine and there won't be a large-scale escalation from Russia," Zelenskyy said during a joint press conference in Kyiv with his Estonian counterpart. "If there will be, we will impose martial law."

Zelenskyy also revealed that he's considering breaking off diplomatic relations with Russia over its recognition of two Russia-backed separatist areas in eastern Ukraine's Donbas region. He said a proposal to do so has been put forward by the Ukrainian Ministry of Foreign Affairs, which he said he's looking at it but has not yet made a decision.

The Ukrainian president also called for Western countries to impose sanctions fast against Russia, saying the situation is developing "very quickly" and that the "first steps" of Moscow's aggression have already been made. Zelenskyy said sanctions should include fully stopping the Nord Stream 2 gas pipeline connecting Russia to Germany.

"The reaction must as quick," he noted. "Sanctions policy is more a powerful policy which can really have an effect on the probable escalation from Russia. Don't wait for it to happen, because already the first steps of this aggression are done. We believe that legally the aggression has already been done."

-ABC News' Patrick Reevell

Kremlin spokesman Dmitry Peskov said Tuesday that the reaction of Western countries to Russia's recognition of two Russia-backed separatist areas in eastern Ukraine is "predictable."

"As for the reaction, it was predictable, foreseeable," Peskov told reporters during a daily call. "We will continue to work and to patiently put across our arguments."

Peskov also claimed not to know anything about possible deployments of Russian "peacekeepers" into the areas overnight and made a comment that suggested the Kremlin may consider the legitimate territory of the separatists to include large parts of eastern Ukraine currently not in their control.

Separatists in the self-declared People's Republics of Donetsk and Luhansk only hold about a third of the territory they claim in eastern Ukraine's Donbas region. The fear is Russia might now back those claims and use it as a pretext to make a larger land grab and destroy Ukrainian forces.

Speaking to reporters Tuesday, Peskov said the Kremlin recognizes the separatist areas "in those borders which they have declared for themselves, when these two republics were declared."

But when asked to clarify, Peskov added: "In those borders, in which they exist and were declared. And were declared and exist."

When pressed if that meant within the "present borders" of the separatist areas, Peskov refused to answer, saying he had nothing more to add.

Peskov also said that Russia's recognition of the areas means the issue of the Minsk agreement is "now off the agenda." He said any negotiations going forward will focus only on Russia's demands for security guarantees that Ukraine not join NATO.

Peskov noted that the United States has not contacted the Kremlin since Russian President Vladimir Putin announced Monday his recognition of the two separatist areas as independent, but that Moscow was "open to diplomatic contacts."

What happens next, he said, is "up to our opponents."

-ABC News' Patrick Reevell

Russia's parliament voted Tuesday to ratify a friendship treaty with two Russia-backed separatist areas in eastern Ukraine.

Lawmakers also added an amendment that brings the Treaty of Friendship into force immediately. The treaty includes a mutual defense pact, which establishes that Russian troops will jointly guard the borders of the self-proclaimed People’s Republics of Donetsk and Luhansk, in a breakaway region of eastern Ukraine known as Donbas.

Lawmakers were still discussing the decrees that Russian President Vladimir Putin signed on Monday night recognizing the two areas as independent. Both the upper and lower chambers of Russia's parliament are expected to vote soon on whether to ratify the orders.

It remains unclear exactly what borders Russia will recognize for the areas. Separatist leaders of the self-declared People’s Republics of Donetsk and Luhansk want to control all of the Donetsk and Luhansk regions in Donbas. But they currently only have about a third, with the rest controlled by Ukraine.

Some Russian officials have suggested Moscow may adopt the position that the separatist areas should include the entire Donetsk and Luhansk regions, thus raising fears that Russian troops will use force to expand the borders.

-ABC News' Patrick Reevell

Top Russian officials on Tuesday morning dismissed new sanctions being imposed by Western countries for Moscow's recognition of the separatist areas in eastern Ukraine.

In an interview with state-owned television channel Russia-24, Russian Foreign Minister Sergey Lavrov said the country was already "used to" sanctions and that more would be imposed regardless of what Moscow does.

"That our [Western] colleagues are trying to push the blame on Russia for the failure of the Minsk agreements, we also understand," Lavrov said. "Our European, American, British colleagues won't stop and won't calm down as long as they haven't exhausted their possibilities for the so-called punishment of Russia."

"They already threaten all possible sanctions. Hellish, or as they say there, 'the mother of all sanctions,'" he added. "Well, we're used to this. The president already noted our position, we know that sanctions will be introduced all the same, in any case. With a basis, without a basis."

Meanwhile, the speaker of Russia's parliament, Vyacheslav Volodin, echoed Lavrov's sentiments during an ongoing session of the lower house, known as the State Duma.

"Yes, sanctions hinder our development. But they would happen anyway. They would happen anyway even if that decision hadn't been taken," Volodin told lawmakers, adding that there are "more important problems."

"Yesterday, our president stopped a war," he said. "It's not a question of territory -- it's a question of the lives of millions of citizens."

-ABC News' Patrick Reevell