Washington (AP) - President Joe Biden added a stop in Poland to his trip to Europe this week for urgent talks with NATO and European allies, as Russian forces concentrate their fire on cities and besiege civilians in an invasion that has lasted nearly a month in Ukraine.

Press Secretary Jen Psaki said in a statement Sunday night that Biden will first travel to Brussels and then to Poland to meet leaders there.

Notably, Poland is an important ally in the Ukraine crisis. It hosts thousands of U.S. forces and welcomes more people fleeing the war in Ukraine - more than 2 million - more than any other country amid the largest European refugee crisis in decades.

Biden is scheduled to head to Warsaw for a bilateral meeting with President Andrzej Duda on Saturday. Psaki said Biden will discuss how the United States, alongside its allies and partners, is responding to "the humanitarian and human rights crisis created by Russia's unjustified and illegal war on Ukraine."

On Monday before his trip, Biden will discuss the war with European leaders. The White House announced Sunday the participation of French President Emmanuel Macron, German Chancellor Olaf Scholz, Italian Prime Minister Mario Draghi, and British Prime Minister Boris Johnson.

White House officials said Biden has no plans to travel to Ukraine. Secretary of State Antony Blinken briefly crossed into neighboring Ukraine during his visit to Poland this month to show solidarity alongside that country’s Foreign Minister Dmytro Kuleba. Poland has been one of the most vocal nations in calling on its NATO fellow members to consider greater involvement to stem the bloodshed.

Russian President Vladimir Putin’s invasion of Ukraine has largely unified the United States, NATO, European allies and allies in Asia and elsewhere. The United States and European governments view Moscow’s military aggression as a threat to their security and strategic interests.

Biden and NATO have repeatedly stated that while the U.S. and NATO will provide weapons and other forms of defensive support to non-NATO member Ukraine, they are determined to avoid any escalation with Kyiv and to avoid a broader war with Russia.

On the other hand, Ukrainian President Volodymyr Zelensky has demanded the U.S. supply his army with more advanced aircraft and air defense systems. NATO and the U.S. have previously rejected his calls to establish a "no-fly zone" over Ukraine to suppress Russian air power, saying it would put Western forces in direct conflict with Russian troops.

After rallying European allies to join comprehensive sanctions on Russia for the invasion initially, Biden’s tasks now include dealing with some NATO members pressing for more direct involvement in the fighting. This includes Poland’s proposals for peacekeeping forces.

In the same context, Biden’s trip includes Thursday’s NATO leaders summit, who will use the meeting to consider strengthening the bloc’s deterrence and defense capabilities immediately and in the long term to address the now openly struggling Putin.

This gathering is not only to show "NATO’s support for Ukraine, but also our readiness to protect and defend all NATO allies," NATO Secretary-General Jens Stoltenberg said on CBS’s “Face the Nation” program Sunday.

Stoltenberg said, "By sending this message, we prevent escalation of the conflict into a full-scale war between NATO and Russia."

Frontline NATO members on the alliance’s eastern flank also demand advanced American and British air defense systems for protection against the types of missile and air attacks Russia is launching on Ukraine.

Estonian Prime Minister Kaja Kallas said, “We need to strengthen our eastern flank of NATO. We have been talking about this for years, but the time has come to act now.”

She added, "We need more capabilities to support ourselves and defend ourselves with air defense systems, which are certainly necessary here, but also the existing forces that act as a deterrent to the Russian army."

Referring to Russia launching missiles "from such a long range that they can also reach Paris from where they are currently firing," Kallas said European leaders must "understand that this defense is our shared issue, and it is not a theoretical discussion but a real-life matter."

Psaki said last week that Biden will also participate in the European Council summit to discuss allies' sanctions on Russia and humanitarian efforts for the millions of Ukrainians displaced by Russian attacks.

She added that his agenda includes a meeting with the Group of Seven leaders to discuss financial and economic sanctions imposed by the West and its allies on Russia due to its invasion.

Edited by: Dima Abu Khair