Key developments on Dec. 22:

• Associated Press discovers over 10,000 new graves in Russian-occupied Mariupol
• Zelensky meets with Polish President in Rzeszów on return from historic trip to US
• US Congress approves amendment to transfer seized assets of Russian oligarchs to Ukraine
• Putin calls Patriot missile systems 'outdated' after US announces supply to Ukraine

An analysis conducted by the Associated Press (AP) has revealed evidence of approximately 10,300 new graves being dug in Russian-occupied Mariupol in Donetsk Oblast since March, when fighting in the port city escalated.

AP arrived at this estimate through the analysis of satellite imagery, video footage, and drone footage. These graves, which occupy over 51,500 square meters, are located in the village of Staryi Krym near the city, as well as in the smaller cemeteries of Manhush and Vynohradne.

Most of the graves lack names and are only marked with hand-scrawled numbers on small plaques. Some graves are designated with more than one number, potentially indicating that multiple bodies are buried there, the analysis reads.

Forensic expert Roland Wessing told AP that the number of graves "doesn't necessarily correspond to the number of Ukrainians killed."

However, AP reported that mass burial sites exhumed in liberated Ukrainian territories often contain multiple sets of human remains per grave and numerous bodies exhibiting signs of violent death.

Read also: Voices of besieged Mariupol: 'It’s not even comparable to hell'

Evidence of a large number of new burials in Mariupol has appeared before. On Dec. 2, U.S. satellite imagery company Maxar published images showing a significant increase in the number of graves at the Staryi Krym cemetery in Mariupol. In early November, the BBC reported that more than 4,600 graves had been dug since the beginning of Russia's full-scale invasion of the city.

The once thriving port city of Mariupol in southeastern Ukraine has been reduced to rubble due to Russia's months-long siege, according to Ukrainian authorities. It has been estimated that some 20,000 civilians have been killed during the siege.

Zelensky meets Duda on a way home from historic trip to US

President Volodymyr Zelensky held a meeting with his Polish counterpart Andrzej Duda on Dec. 22 in Rzeszow, Poland. The meeting concluded Zelensky's first foreign trip since Russia launched its full-scale war in February.

The two leaders "discussed future strategic plans, bilateral relations, and joint actions at the international level next year," according to Zelensky, who referred to Duda as "a friend of Ukraine."

Rzeszow Airport, located 90 kilometers west of Ukraine's border, has been used by Zelensky to travel to Washington, D.C., a day prior.

In Washington, D.C., Zelensky met with U.S. President Joe Biden and delivered a speech to Congress.

In his speech, Zelensky thanked the U.S. for its support and urged lawmakers to continue assisting Ukraine, saying, "Your money is not charity. It is an investment in the global security and democracy that we handle in the most responsible way."

Prior to the face-to-face meeting with Zelensky, the Biden administration announced a new $1.85 billion military aid package for Ukraine, including the first long-sought Patriot air defense system.

The Patriot is a surface-to-air missile system that is the most advanced air defense weapon in the U.S. arsenal. “Specific” NATO allies previously blocked the transfer of the Patriot system for months, NATO Secretary General Jens Stoltenberg recently said.

U.S. forces will train Ukrainian troops to use and maintain the Patriot system in a third country, most likely Germany, but it is unlikely that the air defense system will be delivered to Ukraine before spring, according to the Washington Post.

This assistance will consist of a $1 billion drawdown to provide Ukraine with "expanded air defense and precision-strike capabilities," as well as "an additional $850 million of security assistance," according to the U.S. Secretary of State Antony Blinken.

Following the announcement of the Patriot systems supply to Ukraine, Russian President Vladimir Putin has described them as an “outdated weapon” that Russia will be able to counter.

During a press conference, Putin stated that the Patriot is “quite old” and not on par with Russia’s S-300 system.

During the press conference, Putin also used the word “war” in response to a reporter’s question, according to BBC’s Russian service.

Calling Russia’s actions in Ukraine a war is prohibited in Russia, and citizens can be fined for using it under the law that defines it as “discrediting” the Russian military. The Russian authorities have referred to the invasion of Ukraine as a “special military operation.”

US Congress approves transfering seized assets of Russian oligarchs to Ukraine

Shortly after Zelensky’s trip to Washington, the U.S. Senate on Dec. 22 approved an amendment allowing the transfer of seized assets belonging to Russian oligarchs to the people of Ukraine, CNN reported.

"This amendment would allow the Department of Justice through the Secretary of State to transfer proceeds from seized oligarchs' assets or other sanctioned entities to the people of Ukraine," U.S. Senator Lindsey Graham said. "It will be a godsend to the long-suffering people of Ukraine. It will be a relief to the American taxpayer… It will be a bad day for oligarchs."

The adoption of the amendment is a significant development in the ongoing efforts to hold Russian oligarchs accountable for their role in Russia's invasion of Ukraine.

On Dec. 19, Canada announced it would start seizing approximately $26 million from Granite Capital Holdings Ltd, a firm owned by sanctioned Russian oligarch Roman Abramovich.

Canadian Finance Minister Chrystia Freeland explained that Russian oligarchs have been involved in the "illegal and barbaric invasion of Ukraine," and Canada "will not be a haven for their ill-gotten gains."