KHERSON, Ukraine (Reuters) -Hundreds of Ukrainians were rescued from rooftops on Thursday, two days after waters from a huge breached dam submerged villages, fields and roads in the southern region of Kherson, as Kyiv dismissed reports its counteroffensive had begun.
Drone video showed areas where often only the roofs were visible above the flooding. The region's governor said some 600 square kilometres, or 230 square miles, were under water.
The collapse of the Nova Kakhovka dam came as Ukraine prepared a counteroffensive, likely the next major phase in the war in which tens of thousands of people have been killed, millions uprooted and entire cities reduced to ruins since Russia's "special military operation" began on Feb. 24 last year.
NBC news, citing a senior officer and a soldier near the front lines, said the offensive had begun. The Washington Post cited "four individuals" in the armed forces saying the same thing.
Asked about the reports, a spokesperson for the General Staff of the Ukrainian Armed Forces told Reuters: "We have no such information."
In its daily Ukraine briefing, Britain's defence ministry on Thursday reported heavy fighting along "multiple sectors of the front", adding that Kyiv held the initiative in most areas.
Ukraine's military said the flooding in Kherson had forced Russian troops to retreat by five to 15 km and had "practically halved" Russian shelling.
A senior Russian commander briefed President Vladimir Putin on how his forces had repelled a large-scale Ukrainian attack in the southern Zaporizhzhia region, the TASS news agency reported.
Defence Minister Sergei Shoigu said earlier on Thursday that Russian forces had withstood fierce overnight attempts by Ukrainian troops to break through the frontline in Zaporizhzhia and had inflicted heavy losses on them.
Reuters could not independently verify the battlefield reports.
Russia and Ukraine have traded blame for the bursting of the Soviet-era Kakhovka hydroelectric dam, which sent waters cascading across the war zone of southern Ukraine in the early hours of Tuesday, forcing tens of thousands to flee.
Moscow and Kyiv also accused each other on Thursday of shelling the area as rescue workers in rubber dinghies tried to save people and animals from the still rising flood waters.
Russian shelling wounded at least nine people in Kherson on Thursday as residents were being evacuated, Ukraine's interior ministry said.
The Prosecutor General's office initially said one person had been killed by the shelling but later said no deaths had been reported. A Reuters reporter in Kherson said he could hear what appeared to be artillery fire.
The Kremlin similarly accused Ukraine of shelling Russian rescue workers in the area.
Friends and family of stranded residents posted appeals online with names, photos and GPS locations of residents. The coordinator of a volunteer group on the Telegram messaging app said the appeals were getting more urgent because people were running out of drinking water.
One man, Sergei, told Reuters the last time he spoke with his 83-year-old father-in-law in the Oleshky region was several days before the dam collapse.
"The latest information is that there was a lot of water in the street, as high as a person," he said. "Houses collapsed and went under water."
Ukraine said the floods would leave hundreds of thousands of people without access to drinking water, swamp tens of thousands of hectares of agricultural land and turn at least 500,000 hectares deprived of irrigation into "deserts".
Ukrainian President Volodymyr Zelenskiy, who has appealed for a "clear and rapid" international effort to help flood victims, held emergency talks with officials in Kherson, one of five Ukrainian regions which Moscow claims to have annexed but only partially controls.
The U.N. Office for the Coordination of Humanitarian Affairs said aid agencies had delivered bottles of drinking water, water purification tablets, hygiene kits and jerrycans.
"Drinking water remains the most pressing need," it said.
The Kremlin said Putin had no plans to visit the region but was monitoring the situation.
Putin, without providing evidence, has accused Ukraine of destroying the Russian-controlled dam at the suggestion of its Western allies.
Kyiv said several months ago the dam had been mined by Russian forces who captured it early in their invasion, and has suggested Moscow blew it up to try to prevent Ukrainian forces crossing the Dnipro river in their counteroffensive.
It is not known how many people may have died as a result of the flooding. The Russian-installed mayor of Nova Kakhovka, near the dam site, said on Thursday at least five people had died but the total death toll is sure to be much higher.
Kherson's Ukrainian governor, Oleksandr Prokudin, said 68% of the flooded territory was on the Russian-occupied left bank of the Dnipro River.
The "average level of flooding" in the Kherson region on Thursday morning was 5.61 meters (18.41 ft), he said.
The water level at the Kakhovka reservoir was approaching a dangerous low, the state company overseeing the facility said on Thursday, saying this could affect the nearby Zaporizhzhia Nuclear Power Station and water supply to other regions.
The U.N. atomic watchdog said on Tuesday the plant, Europe's largest, has enough water to cool its reactors for "several months" from a pond located above the reservoir.
Ukrainian and Russian officials have also warned of the danger posed by mines planted during the war and now scattered by the floods.
(Reporting by Reuters bureaux; writing by Gareth Jones and Nick Macfie; editing by William Maclean and Andrew Heavens)