London, Dec 23 : Both Ukrainian and Russian troops are suffering from 'exceptional levels of rat and mice infestation' in some sectors of the frontline, according to UK intelligence. The Ministry of Defence said that rodent populations have risen due to milder temperatures in recent months and plenty of food, The Guardian reported. It said: 'This year's mild autumn, along with ample food from fields left fallow due to the fighting, have likely contributed to the increase in the rodent population." As the weather has become colder, the animals are likely seeking shelter in vehicles and defensive positions. Rodents will add further pressure to frontline combatants' morale.' 'In addition, they pose a risk to military equipment by gnawing through cables ' as recorded in the same area during the second world war. Unverified reports also suggest Russian units starting to suffer from increased sickness cases which the troops attribute to the pest problem', UK intelligence said, The Guardian reported. Ukraine said that its forces have shot down three Russian Su-34 fighter-bomber aircraft on the southern front, hailing it as a success in the 22-month-old war. The Russian military made no mention of the incident. But Russian bloggers acknowledged the loss, and analysts suggested US-supplied Patriot missiles had probably been used. /IANS