CNN  — 

Russian and Ukrainian negotiators agreed that a permanent ceasefire in eastern Ukraine must be observed “unconditionally” following hours-long talks in Paris on Wednesday.

The announcement came after a meeting at the Elysee Palace of the so-called Normandy Format – a four-way conversation between representatives from Ukraine, Russia, Germany and France – that has been trying to broker peace in eastern Ukraine since 2014.

Tensions between Moscow and Kyiv are at their highest in years, with a large Russian troop build-up near the shared borders of the two former Soviet republics – spurring fears that Russia could launch an invasion.

Speaking after Wednesday’s meeting, Moscow’s chief negotiator Dmitry Kozak said the ceasefire must be observed “unconditionally” but that many other issues in eastern Ukraine remained unresolved.

Western officials are continuing to push for a diplomatic solution to the tensions through the full implementation of the Minsk agreements – a ceasefire protocol signed by Ukraine and Russia in 2015.

“We agreed that regardless of different discrepancies of the Minsk agreements that exist between Ukraine and the Donetsk and Luhansk regions, the truce in Donbas must be observed unconditionally,” Kozak said.

He added that the “obligation” to implement such agreements “lies with the armed forces of Ukraine and the armed formations of the (eastern separatists) Donetsk People’s Republic and Luhansk People’s Republic.”

Ukrainian negotiator Andriy Yermak said all parties were in support of a permanent ceasefire and Ukraine was ready to negotiate around the clock to prevent war and to de-escalate tensions around the border.

Yermak called the renewal of the Normandy Format talks – first held after Russia’s 2014 invasion of Crimea – a “very positive signal” and the first such substantive agreement since the end of 2019.

He called talks “really substantial, but not an easy discussion” and while there were still disagreements there was an interest in working through them.

“The work continues and I can tell you that Ukraine as usual is ready to negotiate, to meet 24-7. Because for us, for (Ukrainian) President (Volodymyr) Zelensky, for the entire team, the goal of stopping the war, of ending the war and returning our territories – and today that this also includes easing the tensions – the de-escalation around the Ukrainian border, is the priority,” Yermak said.

Kozak and Yermak said the talks would resume in about two weeks in Berlin.

Russia’s NATO concerns

As many as 100,000 Russian troops have remained amassed at the Ukrainian border, despite warnings from US President Joe Biden and European leaders of serious consequences should Russian President Vladimir Putin order an invasion.

Russia has repeatedly denied it is planning an invasion but has argued that NATO support for Ukraine – including increased weapons supplies and military training – constitutes a growing threat on its western flank.

On Thursday, Russia’s Security Council Deputy Chairman Dmitry Medvedev accused NATO of failing to keep its non-expansion “promise,” saying the alliance had moved closer to Russian borders, state news agency TASS reported.

Medvedev said a process of negotiations on security guarantees is the only way to settle the current tensions between Russia, Ukraine and the West.

“They promised not to expand NATO, but didn’t keep the promise,” Medvedev said, according to TASS. “They say that ‘we did not sign anything.’ But we all know well who and when granted to whom such promises, such assurances.”

Medvedev added: “Everything must be done to avoid any war.”

NATO’s ‘open-door’ policy

As the Normandy Format got underway on Wednesday, the United States delivered a written response to Russia’s concerns over Ukraine. Putin’s central demand is that the US and NATO commit to never admitting Ukraine to the 30-member defense alliance.

US Secretary of State Antony Blinken declined to detail specifics presented to Moscow but said it reiterated the West’s public response to uphold NATO’s “open-door policy.”

“There is no change. There will be no change,” Blinken said of US and NATO support of the alliance’s open-door policy.

“We make clear that there are core principles that we are committed to uphold and defend, including Ukraine’s sovereignty and territorial integrity, and the right of states to choose their own security arrangements and alliances,” he added.

Blinken said the US response to Russia “sets out a serious diplomatic path forward should Russia choose it” and outlines areas where the US has said it sees potential for progress with Russia – arms control, transparency and stability.

CNN’s Radina Gigova, Jeremy Herb, Jennifer Hansler and Kylie Atwood contributed reporting.