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A number of hostages have escaped the Islamist militants who took them captive at a gas facility in eastern Algeria, media and officials say.

Details of the escape and the numbers involved remain unclear, but some 30-40 Algerians and 15-25 foreign nationals were reported to have escaped.

The militants earlier said they were holding 41 foreign nationals.

A siege is ongoing, with Algerian soldiers surrounding the facility near In Amenas.

The kidnappers occupied the complex on Wednesday, after killing a Briton and an Algerian.

Spokesmen for the militants say they have issued a list of demands. One statement purported to be from the hostage-takers called for an end to the French military intervention against Islamist rebels in Mali.

The details on the escapes remain confused.

One Algerian security official told Associated Press news agency that at least 20 foreigners had escaped, including Americans and Europeans.

Algeria's private Ennahar TV channel said that 15 foreigners, including a French couple, had escaped, while another security source told Reuters the total was 25.

Earlier, the Algeria Press Service news agency said 30 Algerian workers had also managed to free themselves.

The Tigantourine gas facility is about 40km (25 miles) south-west of In Amenas, which is close to the Libyan border and about 1,300km (800 miles) south-east of Algiers.

BP operates the gas field jointly with Algerian state oil company Sonatrach and Norwegian firm Statoil.

The companies and the governments of those taken hostage have given few details about the number and identity of those taken captive, citing security reasons.

BP on Thursday confirming that some of its staff were being held but saying that it would not be releasing any details.

The foreign nationals held captive are believed to include British, Japanese, US and Norwegian.

On Thursday, French President Francois Hollande confirmed French nationals were also present at the site, but gave no more details.

Algerian Interior Minister Daho Ould Kablia said that the kidnappers were Algerian and operating under orders from Mokhtar Belmokhtar, a senior commander of al-Qaeda in the Islamic Maghreb (AQIM) before late last year, when he set up his own armed group after apparently falling out with other leaders.

Mr Kablia said the militants wanted to leave the country with the hostages, but he had refused to let them go, adding that there would be no negotiations.

He said a heavily armed "terrorist group" had attacked a bus carrying workers from In Amenas early on Wednesday.

The attackers were repelled by police who had been escorting the bus, but a Briton and an Algerian national had been killed.

The militants then drove to the gas facility's living quarters and took the hostages.

The foreign nationals were being held in one wing of the living quarters, which the security services and army had surrounded, Mr Kablia said.

One worker told France's Le Figaro newspaper the captors had mined the facility.

An Algerian security official told Associated Press the Algerian government was discussing with the US and France whether an international force could help end the stand-off.