North Korea has launched a visceral diatribe against US Democratic presidential candidate Joe Biden, calling the former vice-president a "rabid dog" - while also borrowing the terminology of Donald Trump.Pyongyang is renowned for its vitriol, but the verbal deluge was unusually ferocious even by its own standards.Biden "had the temerity to dare slander the dignity of the supreme leadership of the DPRK", the North's official KCNA news agency said late on Thursday, referring to the country by its official name."Rabid dogs like Biden can hurt lots of people if they are allowed to run about," it went on. "They must be beaten to death with a stick."Doing so will be beneficial for the US also," it added.It was not immediately clear what had provoked Pyongyang's ire, but Biden's campaign released an ad this week condemning Trump's foreign policy, saying that "dictators and tyrants are praised, our allies pushed aside".The voiceover says the word "tyrants" at the exact moment a picture appears of US President Donald Trump and North Korean leader Kim Jong Un shaking hands at their Singapore summit last year.KCNA appeared to cite one of Trump's favoured insults for the candidate - "Sleepy Joe" - when it said Americans called him "Biden not awakened from a sleep".'Time has come for him to depart his life'Biden had shown "a sign of the final stage of dementia", KCNA added. "It seems time has come for him to depart his life."KCNA misspelled the candidate's name as "Baiden" throughout, seemingly reflecting the spelling used in the Korean alphabet.It is not the first time the North has condemned Biden. In May it called him an "imbecile" and a "fool of low IQ" days after he called Kim a "dictator" and "tyrant". The rhetoric underscores its "impatience" with any criticism of Kim, said Cheong Seong-Chang, a senior researcher at the private Sejong Institute."Pyongyang has always loathed hearing its leadership labelled as tyrant or dictator by the outside world," he said. The invective against Biden was "pretty high on the scale", North Korean propaganda specialist Mason Richey of Hankuk University of Foreign Studies told AFP, highlighting the multiple repetitions of the "beating the dog" trope.Trump himself has also been the target of Pyongyang's anger at times.In 2017 the two leaders traded personal insults and threats of war before the diplomatic rapprochement that has seen them meet three times and Trump repeatedly proclaim their personal friendship, although nuclear negotiations remain deadlocked.As tensions mounted, Kim called Trump a "mentally deranged US dotard" whom he would "tame with fire", while KCNA also branded him a "rabid dog".KCNA used the same Korean word previously translated as "dotard" in its article Thursday, although the epithet did not appear in the official English version.