Speaking at a joint news conference with the prime minister of Hungary Tuesday, Russian President Vladimir Putin said Moscow is open to more talks with the West over ongoing tension in Ukraine. However, President Putin also accused the United States and NATO of ignoring Russia’s top security demands. These demands include a halt to NATO’s expansion to Ukraine and other ex-Soviet nations, a freeze on the deployment of weapons there and a rollback of alliance forces from Eastern Europe.

“We should find the way to ensure security of all participants of this process: Ukraine, European countries, Russia,” Putin said. “It is possible to do only through a serious, thoughtful attitude to documents proposed by us.”

The U.S. and its allies have rejected Moscow’s demands, describing them as nonstarters. On Tuesday, Putin said this violates their obligations on integrity of security for all nations. He warned if Ukraine was allowed into NATO, Ukrainian authorities could launch a military action to reclaim control over Crimea or areas controlled by Russia-backed separatists.

“What should we do then, (should we) fight against the NATO bloc? Did anyone think at least something about that? Apparently not,” Putin said.

Despite the U.S. rejecting Russia’s demands, White House Press Secretary Jen Psaki said “the door to diplomacy remains open” on Ukraine. However, she also took issue with how Putin framed the disagreement between the U.S. and Russia.

“When we talk about mutual de-escalation, Russia has 100,000 troops on the border. They are the aggressor,” Psaki said at her daily press briefing. “We are working with NATO countries to make sure they feel secure in this moment. NATO is a defensive alliance. It is not the same thing, and I think we need to be careful about comparing them as the same thing.”

Tuesday’s developments came a day after a tense back-and-forth of accusations at a meeting of the U.N. Security Council. Russia’s ambassador to the U.N. accused the U.S. and others of “whipping up tensions” over Ukraine and said the US had brought “pure Nazis” to power in Kyiv.

“If they had not done this, then we to date would be living in a spirit of good neighborly relations and mutual cooperation,” Vassily Nebenzia said. “However, some in the West just don’t clearly like this positive scenario.”

Meanwhile, the U.S. ambassador to the U.N. accused Russia of “attempting, without any factual basis, to paint Ukraine and Western countries as the aggressors to fabricate a pretext for attack.”