Ukrainian President Volodymyr Zelenskyy said Saturday that counteroffensive and defensive actions were underway against Russian forces, asserting that his top commanders were in a "positive" mindset as their troops engaged in intense fighting along the front line.The Ukrainian leader, at a Kyiv news conference alongside Canadian Prime Minister Justin Trudeau, responded to a question about Russian President Vladimir Putin's comment a day earlier that Ukraine's counteroffensive had started — and Ukrainian forces were taking "significant losses."Related video above: Urgent rescues continue after Ukraine dam collapseZelennsky said that "the counteroffensive, defensive actions are taking place in Ukraine. I will not speak about which stage or phase they are in.""I am in touch with our commanders of different directions every day," he added, citing the names of five of Ukraine's top military leaders. "Everyone is positive. Pass this on to Putin."Trudeau, the first foreign leader to visit Ukraine since devastating floods caused by a breach in a Dnieper River dam, offered up monetary, military and moral support for Ukraine. He pledged $500 million in new military aid, on top of $8 billion that Canada has already provided since the war began in February 2022, and announced $10 million for humanitarian assistance for the flood response.Trudeau said the dam's collapse was "a direct consequence of Russia's war," but he didn't blame Moscow directly.Ukraine's General Staff said Saturday that "heavy battles" were ongoing, with 34 clashes over the previous day in the country's industrial east. It gave no details but said Russian forces were "defending themselves" and launching air and artillery strikes in Ukraine's southern Kherson and Zaporizhzhia regions.At the Zaporizhzhia Nuclear Power Plant, Europe's largest, which is occupied by Russian forces, five out of six reactors were already in a state of cold shutdown, That's a process in which all control rods are inserted into the reactor core to stop the nuclear fission reaction and generation of heat and pressure.Energoatom, the Ukrainian nuclear agency, said in a statement late Friday that there was "no direct threat" to the Zaporizhzhia plant due to the breach of the Kakhovka dam further down the Dnieper River, which has forced thousands of people to flee flooding and also sharply reduced water levels in a reservoir used to help cool the facility.Energoatom said it shut down the final reactor due to that, and also because of shelling near the site that has damaged overhead lines connecting the plant to Ukraine's energy system.With all nuclear reactions stopped, temperatures and pressure inside reactors gradually decline, reducing the required intensity of water cooling of the radioactive fuel. This is a nuclear power plant's safest operating mode. Energoatom employees are still working at the power plant, although it remains controlled by the Russians.The site's power units have not been operating since September last year. The head of the International Atomic Energy Agency is due to visit Ukraine in the coming days.Also on Saturday morning, Ukrainian authorities reported that at least four civilians have died across the country as Russian forces launched Iranian-made Shahed drones, missiles, and artillery and mortar strikes.Ukraine's State Emergency Service reported that three people were killed and more than two dozen wounded overnight in an attack targeting the Black Sea port of Odesa. A spokesperson for Ukraine's southern operational command, Natalia Humeniuk, said two children and a pregnant woman were among those wounded.In Ukraine's northeast, a 29-year-old man was killed as more than 10 drones targeted the Kharkiv region, its governor, Oleh Syniehubov, reported Saturday. He added that at least three other civilians were wounded.In the Poltava region further west, there was damage to a military airfield struck overnight during a Russian drone and missile attack, local Gov. Dmytro Lunin reported. Lunin said no one was hurt. As of Saturday morning, there was no additional comment from the Ukrainian army or officials on the extent of the damage.The Ukrainian air force said that during the night, it had shot down 20 out of 35 Shahed drones and two out of eight missiles "of various types" launched by Russian forces.The fighting and civilian casualties took renewed attention as authorities in southern Ukraine said water levels have been declining in a vast area beneath the ruptured dam.Nearly one-third of protected natural areas in the Kherson region could be obliterated by flooding following the breach of the Kakhovka dam, the Ukrainian environment minister warned Saturday.In a Facebook post, Ruslan Strilets said that the dam's collapse left one national park completely submerged, drained rivers and lakes in other protected areas, and could lead to groundwater rising in parts of the Dnieper delta occupied by Moscow, creating the risk of further flooding.In the city of Kherson, whose outskirts were among the flood-hit areas, the average water level decreased by 31 centimeters (12 inches) during the night, but remained over 4.5 meters (15 feet) higher than usual, regional Gov. Oleksandr Prokudin reported Saturday.Prokudin warned that meteorologists predicted heavy rainfall in the area over the weekend, complicating rescue efforts.The U.N.'s humanitarian aid chief, Martin Griffiths, said in an Associated Press interview Friday that an "extraordinary" 700,000 people were in need of drinking water.In other developments:On Saturday, German Chancellor Olaf Scholz says he wants to continue speaking with Putin — whose order for Russia's invasion of Ukraine has been criticized by many Western leaders — and plans to do so again "soon." Scholz has spoken several times by phone with Putin since the invasion.The chancellor said the basis for a "fair peace" between Russia and Ukraine is the withdrawal of Russian troops. "That's needs to be understood," he said.___Jon Gambrell in Kyiv, Joanna Kozlowska in London and Frank Jordans in Berlin contributed to this story.