Turkmenistan must do more to improve human rights, but the issue would be considered separately from France's economic cooperation with the energy-rich state, Paris' rights ambassador has said.

The ambassador, Francois Zimeray, was also not allowed to visit two rights activists being held in prison in Turkmenistan during his visit on Thursday and Friday to the isolated and authoritarian country.

Zimeray told AFP in an interview that Turkmenistan had made progress on human rights following "catastrophic" earlier years.

"We are talking about a situation where there are many things left to do," Zimeray said. "What happened in the era of (ex-president Saparmurat) Niyazov in the area of human rights was catastrophic for the country."

He noted, however, that "there has been progress and a will to progress." Zimeray highlighted continued violations related to prisons and press freedoms, among others.

President Gurbanguly Berdymukhamedov, a former dentist, has implemented timid reforms since he emerged from obscurity to step to the presidency when Niyazov died of heart failure in 2006.

The central Asian country has signaled it wants to open up to the West to encourage investment in its huge untapped gas reserves.

French construction giant Bouygues has contracts in Turkmenistan worth some two billion euros (2.5 billion dollars).

Zimeray said his message to the country's authorities was that rights and other areas of cooperation would be treated separately.

"It is that we must not oppose human rights with other areas of cooperation," he said of his message.

But the ambassador was also seeking news on two prisoners from the Helsinki Foundation rights organisation and was not allowed to see them.

Zimeray said he spoke with the Turkmen foreign minister on the prisoners, Sapardurdy Khajiyev and Annakurban Amanklychev, who were sentenced to seven years in prison for illegal possession of ammunition after a closed-door trial.

Amanklychev also worked for French documentary company Galaxie-Presse.

Rights groups have criticised the trial that led to their imprisonment.