A senior Ukrainian delegation was visiting Washington just as President Donald Trump said that his Russian counterpart Vladimir Putin warned him by telephone of major retaliation over a daring Ukraine drone strike deep into Russia.

Colonel Pavlo Palisa, who served on the frontlines until President Volodymyr Zelensky in November named him as deputy head of the president's office, presented what he said were findings from Ukrainian military intelligence.

Speaking to reporters after briefing US lawmakers and officials, Palisa said that Russia has set a goal of seizing by the end of September the entirety of Donetsk and Lugansk -- two of the four regions that Russia has claimed to have annexed, and which feature in a Russian proposal that Ukraine terms an ultimatum.

By the end of the year, Russia wants to establish a buffer zone along the Ukraine-Russia border, Palisa said.

"It's interesting, but they have plans even for 2026. The plan for next year is to occupy the whole part of Ukraine which is situated on the left bank of the Dnipro River," he said.

The goal is to "occupy Odessa region and Mykolaiv region, to cut Ukraine's access to the Black Sea," he said.

He did not specify the sources of his assertions.

The Black Sea is militarily and economically critical for Ukraine and a major route for shipments of grain to the developing world.

The vast Dnipro runs through the capital Kyiv and flows to the Black Sea, bisecting Ukraine, whose historical legitimacy has been questioned by Putin.

Palisa said the purported intelligence findings on Russia showed "what they think in reality."

"Unfortunately, they are not speaking about peace. They are preparing for war," he said.

Top Zelensky aide Andriy Yermak, who led the delegation to Washington, encouraged US lawmakers to move forward on a new sanctions bill to "increase the pressure on Russia."

"It's necessary to create the right atmosphere that Russia will go to negotiation -- but go not to make a show, but concrete and real negotiation," Yermak said.

Yermak met US Secretary of State Marco Rubio, who has repeatedly warned that Trump -- who took office vowing quickly to end the war and who briefly cut off support to Ukraine -- is losing patience with Putin.