France was facing a serious militant backlash against its intervention in northern Mali as the hostage crisis in neighboring Algeria deteriorated on Thursday.

French President Francois Hollande confirmed on Thursday that French nationals were among the hostages being held at a gas facility by a militant group linked to al-Qaida, which demanded an end to the French intervention.

The latest Algerian news reports said 34 hostages and 15 kidnappers were killed by Algerian forces.

France remained determined to continue its military push against Islamist militants in Mali. There are now 1,400 French troops on the ground, and a battle between French soldiers and rebel fighters was under way in the city of Diabaly that is likely to continue into Friday, according to the French Defense Minister Jean-Yves Le Drian.

France is also expected to increase its troops in Mali, and the number of French troops deployed in the West African country will gradually reach 2,500, sources close to Le Drian were quoted as saying.

The French defense minister said earlier he will travel to Berlin to talk to his German counterpart about France's military campaign to prevent the rebels from moving south toward the capital, Bamako.

The European Union voted on Thursday in favor of sending training missions to Mali to empower the Malian forces against the Islamic militants, after French Foreign Minister Laurent Fabius warned that all of Europe may be under the threat of terrorism.

Earlier news reports said 20 foreigners, including a French couple, managed to escape from the gas facility in the Sahara desert in addition to 30 Algerian workers who escaped earlier on Thursday.

The French president said on Wednesday that his decision to send troops into Mali was "unavoidable". He also said that the duration of the French military operation there will not last longer than four months.

The latest opinion poll by French newspaper 20 Minutes showed that two-thirds of the French public support the French intervention in Mali. However, an earlier poll by Le Parisien showed 75 percent of the French public in support of the action. Analysts said the French public may gradually lose confidence as the battle continues.

At home, the French government ordered tightened security measures in the country's public buildings and transportation networks in the face of a terrorist threat.

Hundreds of armed soldiers were seen patrolling Paris metros, train stations, airports and tourist sites. Officials have also warned French citizens to be aware of the increased risk of terrorist attack at home and abroad.

Reuters contributed to the story.

Contact the writer at lixiang@chinadaily.com.cn.