WARSAW - U.S. President Joe Biden will argue in a speech in Poland on Saturday that the "free world" opposes Russia's invasion of Ukraine and that there is unity among major economies on the need to stop Vladimir Putin, the White House said.

After three days of emergency meetings with allies of the G7, European Council and NATO, and a visit with U.S. troops in Poland, Biden will meet with Polish President Andrzej Duda.

Biden, who took office last year after a violently contested election, vowed to restore democracy at home and unite democracies abroad to confront autocrats including the Russian president and China's leader Xi Jinping.

Putin's Feb. 24 invasion of Ukraine, which Russia calls a "special operation", has tested that promise and threatened to inaugurate a new Cold War three decades after the Soviet Union unravelled.

In what U.S. officials were billing as a major address in Poland, Biden "will deliver remarks on the united efforts of the free world to support the people of Ukraine, hold Russia accountable for its brutal war, and defend a future that is rooted in democratic principles," the White House said in a statement.

Warsaw, the backdrop for the remarks, was until the collapse of communist rule in 1989 behind the Iron Curtain for four decades, under Soviet influence and a member of the Moscow-led Warsaw Pact security alliance.

Now, Poland is the biggest formerly communist member of the European Union and NATO, the security alliance founded to counter the Soviet Union. The rise of rightwing populism in Poland in recent years has put it in conflict with the European Union and Washington, but the threat of Russia pressing beyond its borders has drawn Poland closer to its Western neighbours.

Biden’s election put Warsaw’s nationalist Law and Justice government in an awkward position after it had set great store in its relationship with his predecessor Donald Trump.

But with tensions with Russia mounting ahead of the Feb. 24 invasion of Ukraine, Duda appeared to seek to smooth relations with Washington. In December, he vetoed legislation that critics said aimed to silence a U.S.-owned 24-hour news broadcaster.

Biden and Duda will meet privately and are expected to address a dust-up over how to arm Ukraine with warplanes, and other security guarantees.

Washington, seeking to avoid a direct conflict with Russia, rejected a surprise offer by Poland to transfer Russian-made MiG-29 fighter jets to a U.S. base in Germany to be used to replenish Ukraine's air force.

Now, Poland wants to accelerate the purchase of U.S.-made Patriot missiles, F35 fighter jets and tanks for its own security, and seek reassurance on NATO commitments to defend its members.

"Above all, we want the unshakable guarantee that the United States provides within the framework of the alliance," the head of the National Security Bureau, Pawel Soloch, said on Friday. "Especially here, to Poland and the countries of the region. If there was an attack on Poland, the USA would defend Poland."

(Reporting by Jarrett Renshaw in Warsaw and Trevor Hunnicutt in Washington; Additional reporting by Nandita Bose in Washington and Justyna Pawlak in Warsaw; Writing by Trevor Hunnicutt; Editing by Heather Timmons and Grant McCool)