The mayor of Mariupol, Vadym Boichenko, who has left the city, claims "traitors" passed on coordinates to Russian forces early on, BBC reported.
"They knew where to shell. There were many traitors who gave coordinates. Everything we had, everything that is considered the critical infrastructure of the city, was destroyed in the first seven days.
"There are 15 power supplies in the city. Even the mayor did not know where they all were. And they knew and in a week destroyed all 15. The city was left without light," he said.
Water points, communication lines and warehouses storing food and medicine were also targeted, Boichenko said, BBC reported.
He accused the "traitors" of being city council deputies from the pro-Russian The Opposition Platform - For Life' party. They now rule the city under the Russian occupation, he said.
He said the destruction of the city's critical infrastructure at the beginning of the invasion was well co-ordinated.
More than 100,000 people are trapped in occupied Mariupol, Boichenko said.
"They don't have clean water. There is no food, no electricity, no medications. Hospitals have been damaged; doctors have been killed. People do not live there, they survive, fighting for food," the mayor said, BBC reported.
Russian forces took control of the southern port city in May after months of relentless bombardment.
Boichenko, who has left Mariupol, said the bodies of many victims still lie in bombed buildings.
"There is a lot of dead in Mariupol. Russians have not cleared the bodies of those they killed in the bombings. Many bodies are still under the ruins According to doctors, this summer in Mariupol will be horrible. And it can take thousands of lives."
"There are no hospitals, no doctors. Russians steal equipment from hospitals that weren't damaged in the fighting and take it to Donetsk.
"People are waiting for several days in a queue for water and fighting for food. Russians forced people to clean ruins in exchange for water. The city is closed. Nobody is let in or out," he said, BBC reported.
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