The top Catholic is also the top tweeter: Pope Francis has the most clout on Twitter

Pope Francis has by far the most clout of any world leader on Twitter because he is so widely retweeted, a study of political use of the social network showed on Wednesday.

With 14 million followers for the nine different language versions of his @Pontifex account, the cyber-savvy pontiff boasts just a third of those notched up by US President Barack Obama.

But that it not the key measure, said Matthias Luefkens, who steers the annual Twiplomacy survey.

"It's not the number of followers which is really important, but the reach, the engagement," he said.

The real benchmark is tweets retweeted by followers to their own network.

Pope Francis wins hands down, with his Spanish-language tweets retweeted more than 10,000 times on average, and his English-language tweets, over 6,400 times.

Obama's 2012 election victory tweet -- a photograph of him embracing First Lady Michelle Obama and the words "Four more years" -- was retweeted a massive 806,066 times.

But on average, @BarackObama gets 1,400 retweets.

Obama's use of social media is credited as a key factor in his landmark 2008 election.

The @BarackObama account, created in 2007, has 43.7 million followers, but is not a US presidential feed and is run by his political campaign staff.

The official @WhiteHouse account has over 4.9 million followers, putting it fifth in the global pecking order, just behind the account of India's new Prime Minister Narendra Modi, and Indonesia's President Susilo Bambang Yudhoyono, who has five million.

@White House was narrowly overtaken on Wednesday by @narendramodi.

"Modi's seen a stratospheric rise," said Luefkens.

Modi, the 63-year-old son of a low-caste tea seller, distances himself from the Delhi elite.

But he is notably tech-aware and has won plaudits from Twitter-watchers for his strategic deployment of it.

Indian officialdom's social media use is a hot topic, as Modi seeks to promote Hindi as the government's official language online, sparking stiff opposition.

While he speaks mostly in Hindi, used by some 40 percent of Indians, Modi's tweets are always in English, preferred for business in a nation with 22 official languages.

Modi, elected in May in a landslide vote, scored 24,000 retweets for his own "India has won!" victory message.

Otherwise, he averages 557.

- Huge impact -

Luefkens is a social media expert at communications firm Burson-Marsteller, which produces the Twiplomacy study.

He said that while television remains the key channel to hit the widest audience, Twitter is an increasingly-powerful tool.

"It helps you to broadcast, and if you broadcast to the right audience, that has huge impact," he said.

The social network enables politicians to create a sense of intimacy and even to interact with one another in public -- sometimes in an undiplomatic manner, seen in a Ukraine-themed tweet fight between the Russian foreign ministry and leaders from Estonia and Sweden.

Twitter is also a tool for leaders to follow one another mutually -- a statement in itself.

France's foreign minister follows 91 peers and world leaders who return the favour via his @LaurentFabius account, putting him at the top of the Twiplomacy table.

Next was the EU's foreign service account @eu_eeas, with 71 mutual connections, and the Swedish foreign minister, with 68 via his @CarlBildt account.

The @WhiteHouse and @BarackObama only follow three peers: the prime ministers of Russia and Norway, and the British government.

Despite taking to Twitter with gusto, politicians are light years behind celebrities.

Top-ranked stars' accounts include @justinbieber with 52.5 million followers, beaten by @katyperry, who has 54 million.