Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty in speech denouncing West

Ukrainian President Volodymyr Zelenskyy said in his nightly address Sunday that he interpreted a lull in fighting after a series of victories by his country's military forces as preparation for the liberation of all of Ukraine.

“Maybe now it seems to some of you that after a series of victories, we have a certain lull," Zelenskyy said.

He went on to say, "this is not a lull. This is preparation for the next series. To the next series of words that are very important to us and must sound. Because Ukraine must be free … all of it."

Ukrainian troops made good on Zelenskyy's call to take back lands claimed by Russian forces with an aggressive counteroffensive over the past week in the country's northeast region.

Ukrainian officials said their forces drove out the Russian in two key areas in the Kharkiv region and are not going to let up.

President Joe Biden said in an interview with CBS' "60 Minutes" that it does not appear China is sending weapons to Russia to use in Ukraine.

“Thus far there's no indication that they've put forward weapons or other things that Russia has wanted,” Biden said in the clip from the interview released Sunday.

That’s consistent with the message his administration has repeatedly shared for months. But it doesn't mean China has stopped helping Russia in other ways, including purchasing Russian oil.

Biden recounted how he had previously told China’s President Xi Jinping that if he thought “Americans and others are gonna continue to invest in China based on your violating the sanctions that have been imposed on Russia, I think you're making a gigantic mistake. But that's your decision to make."

Biden also said he does not think there’s currently a “new, more complicated cold war” with China, as the interviewer, Scott Pelley, put it.

-ABC News' Ben Gittleson

Ukraine's ambassador to the U.S., Oksana Markarova, accused Russia on Sunday of committing "war crimes of massive proportions" after a mass grave was discovered in Ukraine.

"It's tortures, rapes, killings. War crimes of a massive proportions," Markarova claimed in an interview with ABC "This Week" co-anchor Jonathan Karl. "That's why we need to liberate the whole territory of Ukraine as soon as possible because clearly Russians are targeting all Ukrainians. Whole families. Children. So, there is no war logic in all of this. It's simply terrorizing and committing genocide against Ukrainians."

Ukrainian President Volodymyr Zelenskyy said in an address on Thursday that a mass grave was found in the recently recaptured territory of Izyum. Over 400 bodies could be buried in the site, according to Ukrainian officials.

Markarova said the majority of the bodies recovered from the site are Ukrainian, including entire families. She also said most of the remains showed "clear signs of torture."

She said an investigation of the mass grave is underway and that with the assistance of the United States her country is continuing to prepare national and international criminal cases against Russia.

Russia has repeatedly denied targeting civilians, despite evidence otherwise.

"It's so important for everyone to see the true face of this aggression and terrorist attack Russia is waging," Markarova said.

-ABC News' Kelly Livingston

Russian President Vladimir Putin on Friday vowed to press his attack on Ukraine, despite the latest counteroffensive with Ukraine claiming it regained control of almost 400 settlements, according to the the Associated Press.

Putin met with Turkish President Recep Tayyip Erdogan in Samarkand, Uzbekistan Friday, on the sidelines of a security alliance summit, to discuss economic cooperation and regional issues, including the agreement allowing Ukrainian grain exports to resume, which was brokered by Turkey and the United Nations, according to the AP.

Putin told reporters the "liberation" of Ukraine's entire eastern Donbas region remained Russia's main military goal and that he sees no need to revise it, saying "we aren't in a rush," according to the AP.

Asked about the Ukrainian counteroffensive, Putin said, "Let’s how it develops and how it ends," according to the AP.