An Islamic group headed by influential cleric Sheikh Yusuf al-Qaradawi on Thursday criticized France's "haste" in launching an offensive against Islamists in Mali, warning of "dangerous consequences."

"Military intervention has dangerous consequences, whether in killing, destruction, displacement... and famine, which Mali is already suffering from," the Qatar-based International Union of Muslim Scholars said in a statement.

Mokhtar Belmokhtar, the one-eyed Islamist whose men seized dozens of hostages in a deadly attack on an Algerian gas field, is a wily desert fox branded as a terrorist by some but perhaps just a common brigand.

He was born in 1972 in the ancient desert city of Ghardaia, 600 kilometers (370 miles) south of the Algerian capital, noted for its date production and manufacture of rugs and fabrics.

An Algerian air strike killed 34 hostages, some of them Westerners, and 15 of their Islamist kidnappers at a desert gas field on Thursday, the ANI news agency quoted a spokesman for the kidnappers as saying.

"Thirty-four hostages and 15 kidnappers were killed in an (air) raid by the Algerian army," the spokesman said in remarks that have not been independently confirmed.

Islamist fighters waging a war against French troops in Mali are deploying child soldiers and using the population as a shield against the offensive, a Malian army source said Wednesday.

"These people (the Islamists) have two strategies: using the population as a shield and child soldiers as fighters," the military leader said on condition of anonymity.

The United States on Wednesday confirmed that American citizens are among hostages being held in Algeria after an attack by Islamist militants near a southern gas field.

"The best information that we have at this time is that U.S. citizens are among the hostages," State Department spokeswoman Victoria Nuland said, but she added that for the safety of the people concerned she would not give further details on how many were held and who they were.

The International Criminal Court on Wednesday opened a war crimes probe on Mali, where French troops are fighting Islamist rebels who have been occupying half the country since April last year.

"Different armed groups have caused havoc and human suffering through a range of alleged acts of extreme violence," the Hague-based court's chief prosecutor, Fatou Bensouda, said in a statement.

Chancellor Angela Merkel on Wednesday pledged two German Transall military transport planes for the mission against Islamist rebels in Mali, warning that allowing "terrorism" there would endanger Europe.

Speaking to reporters after a meeting with Ivory Coast President and ECOWAS chairman Alassane Ouattara, Merkel said Berlin would make two planes available "in a short timeframe" to ferry African troops into the capital Bamako.

Algeria, which has opened its airspace to French warplanes hitting Islamists in northern Mali, was targeted Wednesday in a deadly revenge attack in which militants seized 41 Western hostages.

The Islamists, who said they entered Algeria from northern Mali, told Mauritanian media they were holding 41 Westerners, among them French, British and Japanese citizens, as well as seven Americans, at a southern gas field.

The Organization of Islamic Cooperation on Wednesday expressed support for the French-led Mali military operation, a day after calling it "premature" and urging a ceasefire.

OIC chief Ekmeleddin Ihsanoglu "has reaffirmed the full support and solidarity with the Republic of Mali in its efforts to expeditiously recover areas in the north of its territory under the control of armed groups in order to restore its national unity and territorial integrity," a statement said.

French troops engaged in close combat with Islamist rebels on Wednesday in Mali as al-Qaida-linked fighters attacked a gas plant in neighboring Algeria taking several foreigners hostage.

After days of airstrikes on Islamist positions in the territory they have occupied since April, French and Malian troops battled the insurgents in the small town of Diabaly, some 400 kilometers (250 miles) north of Bamako.