Polish President To Address Ukraine's Parliament During Surprise Kyiv Trip.

Polish President Andrzej Duda addresses lawmakers during a session of the Ukrainian parliament in Kyiv on May 22.

Ukraine continued to rule out any "concessions" to Russia despite the intensive onslaught by Kremlin forces and as Polish President Andrzej Duda, in a surprise visit, urged Kyiv not to give in to the demands of Russian President Vladimir Putin.

"The war must end with the complete restoration of Ukraine's territorial integrity and sovereignty," Ukrainian presidential chief of staff Andriy Yermak said in a Twitter post on May 22.

"That is, our victory. Our common victory with the civilized world. After all, today [Ukraine] is defending not only itself," he said, adding that it was defending all of Europe.

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Yermak's tweet, consistent with previous Ukrainian remarks, came as Duda became the first foreign head of state to address Ukraine’s parliament since Russia invaded Ukraine on February 24 as he sought to bolster resolve and offer support for the country's EU hopes.

In his speech to the Verkhovna Rada, Duda said that "worrying voices have appeared, saying that Ukraine should give in to Putin's demands. Only Ukraine has the right to decide about its future."

He added that surrendering any Ukrainian territory would be a blow to the entire West and repeated Poland’s firm support for Ukraine’s membership in the European Union.

Shortly after his address, and another one by Ukrainian President Volodymyr Zelenskiy, air-raid sirens were heard across the capital, a sign that dangers remain there, although the front lines have shift to the east and south of Kyiv.

In April, Duda visited Kyiv for talks with Zelenskiy as part of a delegation with the presidents of Lithuania, Latvia, and Estonia.

During this trip, Duda offered strong support for Ukraine's bid to join the EU, despite reluctance to move quickly by some major powers, including France and Germany.

Duda said those who "shed their blood" in the fight to belong to Europe must be respected -- "even if the situation is complicated, even if there are doubts."

"I have no doubt that the European Union will make such a gesture," he said.

He pointed to a European Council decision on Kyiv’s candidate status set for June 24, saying it would be "extremely important, above all psychologically and politically."

Zelenskiy on May 21 rejected a suggestion by French President Emmanuel Macron that Ukraine be invited to join some form of “associated” political community with the EU.

“We don’t need such compromises,” Zelenskiy said in Kyiv during a joint press conference with visiting Portuguese Prime Minister Antonio Costa. “Because, believe me, it will not be a compromise with Ukraine in Europe. It will be another compromise between Europe and Russia.”

On May 22, France’s European affairs minister told French radio that any bid by Ukraine to join the EU would likely take at least 15 to 20 years to finalize.

"We have to be honest. If you say Ukraine is going to join the EU in six months, or a year or two, you're lying," Clement Beaune told France’s Radio J. "It's probably in 15 or 20 years -- it takes a long time."

Duda’s visit came as Russian forces stepped up offensive operations across broad swathes of eastern Ukraine. There was heavy shelling around the northeastern cities of Severodonetsk and Lysychansk, Ukraine’s military said.

Ukraine’s lead negotiator, presidential aide Mykhaylo Podolyak, told Reuters on May 21 that Kyiv had ruled out any cease-fire agreement with Russia that included ceding any Ukrainian territory.

“The war would not stop,” he said, in the event of such an agreement. “It would just be put on pause for a time. They’ll start a new offensive, even more bloody and large-scale.”

WATCH: Burned-out armored vehicles, notebook doodles, shattered weapons, and the wreckage of a fighter jet are among items belonging to the Russian military to go on display at Ukraine's National Military History Museum in Kyiv.

Zelenskiy said in a video address to the nation the same day that the war “will only definitively end through diplomacy.”

Meanwhile, U.S. Secretary of State Antony Blinken and newly appointed French Foreign Minister Catherine Colonna have agreed on the importance of continuing “steadfast support” for Ukraine, the State Department said.

The two also discussed the importance of “maintaining significant costs” on Russian President Vladimir Putin “for his war of choice,” a statement released on May 22 said.

The two diplomats also discussed steps Washington and Paris could take to best support Finland and Sweden’s recently announced bids to join NATO, decisions that have angered Putin, who said he invaded Ukraine in part to prevent the expansion of the Western military alliance.

“Both agreed on the need to respond to the urgent food security and nutrition needs of millions of people in vulnerable situations around the world, which have been exacerbated by Russia’s continued brutal war in Ukraine,” the statement said.

French President Emmanuel Macron on May 20 named Colonna -- Paris’s current ambassador to Britain -- as foreign minister following his reelection as French leader. She replaced veteran Foreign Minister Jean-Yves Le Drian.

With reporting by AP and Reuters