Saparmurat Niyazov, the colourful but authoritarian President of Turkmenistan, has died suddenly after 21 years of iron-fist rule which crushed his opposition and created a cult of personality that saw cities and even a meteorite named after him.

Mr Niyazov, who made himself President-for-life in 1999, died early today of a heart attack aged 66, according to a statement by the state-controlled media.

"He died in the night due to sudden cardiac arrest," the televised announcement said, showing the leader’s portrait against the backdrop of the national flag.

The announcement saw flags being lowered throughout the capital, while all 23 state-owned newspapers halted publication, and the government cancelled public celebrations for the new year. "We are all in shock," a senior government official said.

Mr Niyazov’s death leaves Turkmenistan – which contains the world’s fifth-largest reserves of natural gas – facing an uncertain future, with no designated heirs in line to take over. Analysts predict a fierce struggle involving forces from within and outside, grappling for control of the energy-rich state.

State officials said that interim power will pass to the deputy prime minister, Kurbanguly Berdymukhammedov, with a final decision on a successor to be made by the country’s highest representative body on Boxing Day.

Members of his family - led by his son Murat Niyazov - are potential successors according to observers, but the extent of their influence on public life in Turkmenistan is not clear.

The Government moved quickly to stress that "the interior and foreign policies of Turkmenistan will be maintained", but opposition groups – exiled and suppressed under Mr Niyazov – vowed to unite and return to their country.

"An opposition coalition government must be formed," Nurmukhammed Khanamov, leader of the exiled Republican Party, was quoted as saying by RIA Novosti news agency.

Parakhad Yklymov, another Turken activitist, based in Sweden, told Reuters: "In Turkmenistan there is no opposition, they all sit in prisons or under home arrest. But outside the country opposition exists and it is coming back."

Mr Berdymukhammedov had been named to lead the state commission for organising Mr Niyazov’s funeral on Christmas Eve - a post that in Soviet practice was often reserved for likely successors.

He also represented the nation at a summit of the former Soviet Commonwealth of Independent States in Belarus last month – a further sign of his importance in state affairs.

Times Recommends

• Henning Mankell: ‘If Wallander was alive, I wouldn’t be a friend of his’
• Secret society's skull and crossbones for sale
• Nigerian leader vanishes after medical treatment