"I have a packed work schedule. Even my daughters I only see once or twice a month, and then I need to pick my moment," Putin said.

Asked what country his daughters live in, the former KGB officer said: "In Russia, where else? Of course, they live in Moscow. We meet at home."

According to unconfirmed reports this summer, Maria was forced to flee her home in the Netherlands after a missile allegedly supplied by Moscow downed Malaysia Airlines flight MH17 in eastern Ukraine, killing 298 people, mostly Dutch nationals.

The mayor of the Dutch city of Hilversum, which lost several inhabitants in the July 17 disaster, called for her to be deported, before he retracted his "unwise" comments.

Ukrainian activists even published photos and the address of her purported "luxury apartment", urging people to protest outside.

Yekaterina was reportedly set to marry the son of a South Korean general in 2010 but the rumour was denied by Putin's spokesman.

According to previous reports, both Maria and Yekaterina attended St Petersburg State University. Maria is reported to have studied biology, while her sister majored in Asian studies.

Putin is never officially photographed with his daughters, whose secrecy is in marked contrast to the high profile Tatyana Yumasheva, daughter of his predecessor Boris Yeltsin.

Putin used the interview to hone his image for clean living, saying his favourite drink is "ordinary [black] tea", served in a thermal travel mug.

He said he was too busy to have many friends. "All the same I don't feel lonely. However strange that sounds."

Putin's own love life has long been the subject of rumours in a country where the media is largely under tight state control and there is little independently verified information on the lives of Putin's inner circle.

He was linked to former Olympic gymnast Alina Kabayeva several years before his divorce from his wife of 30 years, Lyudmila, a former Aeroflot stewardess, was announced last year.

In 2008 newspaper reported Putin was about to wed Kabayeva, who is 31 years his junior. The newspaper's owner closed it shortly afterwards.

"There is a private life in which no one should interfere. I've always had a low opinion of those with snotty noses and erotic fantasies who delve into the lives of others," Putin said at the time.

Kabayeva is now the head of a powerful pro-Kremlin media group, after resigning her seat in the Russian parliament, as an MP for Putin's United Russia Party.

Lyudmila Putina has all but vanished from public view after the divorce in April.

Putin promises to step down by 2024

Vladimir Putin will not remain Russia's president for life and will step down in line with the constitution no later than 2024, he said.

Staying in office beyond that would be "detrimental for the country and I don't need this", he told the Tass news agency.

Putin, 62, has effectively led Russia since he was first elected in 2000. He stepped aside after two four-year terms to abide by constitutional term limits, but retained power as prime minister and was elected president again in 2012 to a six-year term. A decision on whether to run for a fourth term in 2018 will depend on the situation in the country and his "own mood", he said.

He said Western sanctions against Russian individuals and businesses over Ukraine were an attempt to punish his friends and were "driven by a desire to cause a split in the elite and then, perhaps, in society". But to the West's chagrin, Putin said, Russian society remained consolidated behind him.

He acknowledged that not all Russians support him, which he said was fine as long as their criticism was constructive and they did not violate the law. But he said his government would crush anyone who tried to weaken the state, describing them as "bacteria".

"They sit inside you, these bacilli, these bacteria, they are there all of the time," Putin said. "But when an organism is strong, you can always keep back the flu because of your immune system."