Iran on Sunday announced that 32 people, including two Bangladeshis, who went missing after a ship and an oil tanker collided off at the East China coast last week, were presumed dead.
The tanker that had been burning for more than a week sank on Sunday, the Chinese Transportation Ministry said.
According to Iranian state media, only three bodies have been recovered so far.
"There is no hope of finding survivors among the members of the crew," Mohammad Rastad, spokesman for the Iranian rescue team said.
"Despite our efforts, it has not been possible to extinguish the fire and recover the bodies due to repeated explosions and gas leaks," he said.
On Saturday, Chinese rescuers recovered the tanker's "black box", the transport ministry said without specifying exactly what had been retrieved.
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Earlier, it was reported that a majority of the 136,000 tonnes of oil condensate that was being carried by the tanker, had caught fire.
The Daily Star had quoted the transport ministry in China, as saying that apart from the two Bangladesh crew members, 30 Iranians were declared missing. Twenty-one Chinese crew have been rescued, it added in a statement.
Foreign media reports had said that the accident happened 160 nautical miles east of Shanghai.
China had reportedly sent specialised "cleaning ships" to the mishap site to minimise environmental damage.