Paris, France (CNN) -- A tape of a man claiming to be Osama Bin Laden threatening France appears to be authentic, the French Foreign Ministry said Thursday.

Bin Laden warned France to get its troops out of Afghanistan and not to oppress Muslims at home in a tape broadcast by the Al-Jazeera network Wednesday.

"If you want to tyrannize and think that it is your right to ban the free women from wearing the burqa, isn't it our right to expel your occupying forces, your men from our lands by striking them by the neck?" the speaker demands, in reference to recently passed French legislation barring women from covering their faces in public.

"This message only confirms the reality of the terrorist threat against which the French authorities have taken and continue to take appropriate measures," the ministry said in a statement Thursday.

"French authorities are fully mobilized to secure the release of seven hostages kidnapped in Niger on September 16. These statements by Bin Laden will not affect our assessment of the situation of our hostages and obviously will, therefore, not erode our efforts to secure their release. France will continue to fight against terrorism alongside its partners," the ministry said.

Five French nationals were kidnapped last month along with a person from Togo and one from Madagascar. A photograph of them was posted September 30 on a website linked to al Qaeda.

French authorities are treating the Bin Laden message "very, very seriously," CNN counterterror analyst Paul Cruickshank said.

An opposition lawmaker Wednesday urged "contempt towards these terrorists.

"All of this is derisory, contemptible. We must take this message for what it is but we must stand together in France, all French, whatever the circumstances and whatever our differences," said Francois Loncle, a Socialist Party member of the foreign relations committee of the National Assembly said on RTL radio.

The demands of the speaker on the tape are clear.

"The only way to safeguard your nation and maintain your security is to lift all your injustice and its extensions off our people and most importantly to withdraw your forces from Bush's despicable war in Afghanistan," the speaker says.

The tape is audio only. The speaker does not appear. CNN was not able to confirm that it is really Osama Bin Laden, the head of al Qaeda.

But fake Bin Laden tapes have never been broadcast, U.S. intelligence experts say.

"As you kill us, you will be killed. As you imprison us, you will be imprisoned, and as you threaten our security, we will threaten your security and the initiator of the injustice is the true aggressor," the speaker says.

The France's terror alert level is red, the second highest, authorities say. It did not change immediately in response to the new tape.

Paris has been on edge lately, with the Eiffel Tower having been evacuated twice.

Al Qaeda has issued a series of threats against France in the past, and French citizens have been killed by groups in Africa claiming affiliation with Bin Laden's group.

Bin Laden is still providing strategic direction to al Qaeda from a base somewhere in Pakistan, Cruickshank said.

"He is still involved in actual plotting... signing off on (an) operation, Western intelligence authorities believe," he said.

But there have been only two successful attacks on the West since September 11, 2001, he pointed out.

Commuter trains in Madrid, Spain, were bombed in March, 2004, killing 191 people. Public transport in London, England, was bombed in July, 2005, killing 52, plus four suicide bombers.

France has 3,750 troops in Afghanistan, according to NATO's International Security Assistance Force.

French lawmakers approved a ban on full-face veils in September, citing security concerns and saying they violated women's human rights. The ban is scheduled to come into effect in the spring.