Even before this summer's war over South Ossetia it was clear that Vladimir Putin loathed Mikheil Saakashvili, Georgia's pro-US president. The Kremlin leader's hatred wasn't just political – it was personal.

Just how personal was revealed yesterday when it emerged that Putin had threatened to hang Saakashvili "by the balls". Putin made his 'balls' remarks to France's president Nicolas Sarkozy in August, after Sarkozy flew to Moscow to broker a peace deal

With Russian tanks closing in on Georgia's capital Tbilisi, Sarkozy told Putin that he simply couldn't overthrow the democratically-elected Georgian regime. According to Sarkozy's aide Jean David Levitte, Putin was unbothered by this. He declared simply: "I am going to hang Saakashvili by the balls."

Why, though, does Putin detest Saakashvili so much? During an interview in August, just after the conflict ended, Saakashvili told me that his last encounter with Putin around a year before the war in the Caucasus had ended badly.

Saakashvili said he complained to Putin about Russia's growing interest in Georgia's breakaway provinces of South Ossetia and Abkhazia, adding that he, Saakashvili, enjoyed the support of western leaders.

Putin responded in earthy terms. According to Saakashvili, Putin replied that he could stick this support, well – up his arse. Aides to Georgia's president wearily acknowledge that the personal animosity between both men was an important factor in August's conflict.

Russia's invasion of Georgia, one said, was designed to destroy the country's territorial integrity and overthrow its pro-western government. More than this though it was about Misha, as Saakashvili is known. "Putin hates Misha. He really hates him," one aide told me.

There are other explanations for Putin's balls outburst. In Russia, of course, nobody criticises Putin. One of his earliest acts as president was to get rid of Russia's equivalent of Spitting Image after it mocked him.

The Kremlin controls all state-TV channels, ensuring that critics of the president do not appear. Political humour in Russia is almost non-existent. Political cartoonists have a tough job. During an EU-Russia summit meeting in Siberia this June I asked one senior EU leader whether he thought Putin had a sense of humour.

He replied: "Yes. But his humour is rather cruel. He only has a sense of humour if the joke is at someone else's expense."

Impulsive and bonhomous, Saakashvili, meanwhile, is clearly the temperamental opposite of Putin, the sober and clinical former KGB colonel. Before the war Georgia's leader took every opportunity to lampoon Putin's regime, a trait described by someone as climbing to the top of the hill and mooning at Russia.

Putin is said to have been particularly incensed after Saakashvili described him as "Liliputin" - a mocking reference to Putin's diminutive height. No wonder, then, that Putin was keen to hang his Georgian adversary by the balls.

According to Levitte, Sarkozy's diplomatic advisor, the French president misheard the balls remark. Sarkozy replied: "Hang him?" Putin then replied: "Why not? The Americans hanged Saddam Hussein." Sarkozy tried to dissuade Putin from this course of action, reasoning: "Yes, but do you want to end up like (US president George W.) Bush?"

Putin was briefly silenced before responding: "Ah, you have scored a point there!" Today Putin's press secretary Dmitry Peskov conceded that "tough rhetoric" had been used during negotiations between Putin and Sarkozy over a ceasefire deal. There was no mention of the word balls, though.