As Iran continues to defy Western efforts to prevent it from obtaining a nuclear weapon, it appears the Islamic Republic has found itself a new enemy.

London's Times newspaper reported Tuesday that Tehran's environmental agency is dealing with rats running rampant in 26 districts of the Iranian capital.

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According to the agency, as poison is proving less and less effective, sniper teams are being used instead.

The creatures have grown increasingly resistant to rat poison, the Times said, so the council is resorting to less conventional means and has deployed 10 sniper teams who go out at night to hunt their prey with rifles equipped with infra-red sights.

“We use chemical poisons to kill the rats during the day and the snipers at night, so it has become a 24/7 war,” said Mohammad Hadi Heydarzadeh, head of the environment agency.

According to the report, the rats are whoppers, some weighing as much as 4.5 kilograms (10 pounds) pounds, and are overrunning Vali Asr, the avenue that dissects the city from north to south and is lined with restaurants and fast-food outlets.

Ismail Kahram, a university lecturer and an environmental adviser to the city council, told the website Qudsonline.ir that the rats “seem to have had a genetic mutation, probably as a result of radiations and the chemical used on them.

“They are now bigger and look different. These are changes that normally take millions of years of evolution. They have jumped from 60 grams (960 ounces) to five kilos (11 pounds), and cats are now smaller than them,” said Kahram.

According to the report, so far the snipers have killed a mere 2,205 rats, but the council is planning swiftly to increase the number of teams to 40.