SERGEI SUPINSKY/AFP via Getty Images(NEW YORK) -- More than six months after Russian President Vladimir Putin launched an invasion into neighboring Ukraine, the two countries are engaged in a struggle for control of areas throughout eastern and southern Ukraine. Ukrainian President Volodymyr Zelenskyy, whose forces began an offensive in August, has vowed to take back all Russian-occupied territory. But Putin in September announced a mobilization of reservists, which is expected to call up as many as 300,000 additional troops. Here's how the news is developing. All times Eastern: Nov 19, 12:49 PM EST US warns Russia's eroding situation could lead to 'more nuclear saber-rattling' Russia's eroding situation could lead Russian President Vladimir Putin to "more nuclear saber-rattling," U.S. Defense Secretary Lloyd Austin warned Saturday. "The ripples of Russia's invasion has traveled far beyond Europe. Beijing, like Moscow, seeks a world where autocrats can stamp out the flame of freedom," Austin said while addressing the Halifax International Security Forum. Austin said the deadly explosion in Poland this week was the result of the "recklessness of Putin's war of choice." "Russia's invasion offers a preview of a possible world of tyranny and turmoil that none of us would want to live in. And it's an invitation to an increasingly insecure world haunted by the shadow of nuclear proliferation," Austin said. He went on, "Putin's fellow autocrats are watching and they could well conclude that getting nuclear weapons would give them a hunting license of their own. And that could drive a dangerous spiral of nuclear proliferation." Nov 18, 2:36 PM EST Trace of explosives found at Nord Stream pipelines, Swedish prosecutors say An investigation into the cause of a leak from the Nord Stream pipelines in the Baltic Sea revealed "extensive damage" and several "foreign items," some with detectable "explosive residue," the Swedish Security Service and a prosecutor said Friday. "The advanced analysis work is still in progress – the aim is to draw more definitive conclusions about the Nord Stream incidents. The investigation is extensive and complex and will eventually show whether anyone can be suspected of, and later prosecuted for this," prosecutor Mats Ljungqvist and the Swedish Security Service said in a statement. Several blasts near the Nord Stream 1 and Nord Stream 2 gas pipelines on Sept. 26 caused leaks. Officials are still investigating the cause of the blasts. Major pipelines which supply natural gas from Russia to Europe, were shut off in September. While they were not in use at the time of the blast, the pipelines were filled with natural gas. Nov 17, 1:53 PM EST Russian strike on Ukraine's Dnipro leaves 23 injured A Russian missile strike on the Ukrainian city of Dnipro has left 23 people injured, 15 of whom are in hospital. One person is in grave condition, according to Valentyn Reznichenko, the governor of the Dnipropetrovsk Oblast. Local officials earlier said the strike had left at least 14 people dead. Air raid sirens went off in several Ukrainian cities including Odessa and Zaporizhzhia. Officials said four missiles were shot down in Kyiv. -ABC News' Will Gretsky, Joe Simonetti and James Longman Nov 17, 1:23 PM EST Polish officials grant Ukrainian investigators access to site of missile explosion Polish authorities have granted Ukrainian investigators access to site of the missile explosion, as an investigation into the origin of the missile continues, according to Jakub Kumoch, an aide to Polish President Andrzej Duda. Ukrainian President Volodymyr Zelenskyy, who denies that the missile originated from Ukrainian air defense, has been requesting access to the site. -ABC News' Will Gretsky Nov 17, 12:57 PM EST Ukrainian officials refute US estimates on number of killed, injured soldiers Top Ukrainian security officials are refuting U.S. estimates of how many Ukrainian soldiers have been killed or injured in the war. Last week, the U.S. chair of the Joint Chiefs of Staff, Gen. Mark Milley, said around 100,000 Ukrainian troops have been killed or injured. Ukrainian officials are now saying that figure is "not entirely true." Oleksiy Danilov, Ukraine's secretary of National Security and Defense Council, said the casualty figures are "definitely not those." -ABC News' Tom Soufi Burridge Nov 17, 11:35 AM EST Biden says Zelenskyy's statements on Poland missile incident are 'not evidence' President Joe Biden was asked by reporters Thursday what his reaction was to Ukrainian President Volodymyr Zelenskyy denying that the missile that landed in Poland was Ukrainian. "That's not the evidence," Biden responded. On Wednesday, the White House told reporters it had "seen nothing" to contradict the assessment that the explosion in Poland was likely caused by a Ukrainian defense missile. "We will continue to assess and share any new information transparently as it becomes available. We will also continue to stay in close touch with the Ukrainians regarding any information they have to fill out the picture," National Security Council spokesperson Adrienne Watson said in a statement. -ABC News' Lauren Minore Nov 16, 3:00 PM EST Zelenskyy disputes claim that missile blast in Poland was fired by Ukraine's air-defense system Ukrainian President Volodymyr Zelenskyy pushed back Wednesday against claims that a Ukrainian defense missile landed in Polish territory on Tuesday, killing two. Polish President Andrzej Duda said Wednesday that the Russian-made missile likely came from Ukraine's air-defense system. U.S. Defense Secretary Lloyd Austin said he backs Duda's assertion. -ABC News' Luis Martinez, Matt Seyler and Tom Soufi Burridge Nov 16, 12:48 PM EST Ukrainian air defense missile likely caused deadly blast in Poland: US official The U.S. believes that the missile strike was likely due to a Ukrainian air defense missile, according to a U.S. official. The missile strike killed two Polish civilians. -ABC News' Luis Martinez Nov 16, 9:08 AM EST CIA director met with Zelenskyy in Kyiv after meeting Russian counterpart CIA Director Bill Burns traveled to Kyiv to meet with Ukrainian President Volodymyr Zelenskyy on Tuesday, following a meeting with his Russian counterpart in Turkey, according to a U.S. official. Burns was in the Ukrainian capital during Tuesday's widespread Russian missile strikes. "He is safe and was safely in the U.S. embassy during the strikes," the official said. While in Kyiv, the official said, Burns "discussed the U.S. warning he delivered to the head of Russia's SVR not to use nuclear weapons and reinforced the U.S. commitment to provide support to Ukraine in its fight against Russian aggression." Nov 16, 7:27 AM EST Polish police share photo of large crater from missile Poland's national police force posted an image on Twitter on Wednesday purportedly showing the site of Tuesday's missile blast, which left two people dead. The photo showed authorities collecting evidence from a large crater in the ground, alongside debris and a destroyed vehicle. The Polish Police said in the tweet that its "officers have been securing the area" since the blast happened in the southeastern village of Przewodow, which is close to the border with Ukraine. An investigation into the incident is ongoing, but Polish President Andrzej Duda said Wednesday that the projectile was "probably a Russian-made S-300 missile" and, so far, appeared to be an "unfortunate accident." W #Przewodów, gdzie doszło do wybuchu policjanci od początku zdarzenia zabezpieczają teren. Policyjni eksperci m. in. z @CBSPolicji, #CLKP, Biura Kryminalnego @PolskaPolicja wspólnie z innymi służbami szczegółowo wyjaśniają okoliczności zdarzenia i zabezpieczają dowody. pic.twitter.com/ohBP0rT4u7 — Polska Policja 🇵🇱 (@PolskaPolicja) November 16,