French security forces Monday stormed an Air France plane hijacked from Algiers, setting off an explosion and starting an exchange of gunfire as the aircraft sat on the tarmac at Marseille's airport.

The pilot and co-pilot of the hijacked plane, seized Saturday by armed Islamic radicals in Algiers, were killed, reporters listening to police radio said.The assault occurred after hijackers killed a fourth hostage and dumped the body out of the plane.

Live television showed a white flash burst from the rear of the plane with sparks flying at 5:20 p.m. (9:20 a.m. MST).

Television reporters said gunshots were also heard as several fire engines rushed to the rear of the plane as dusk fell at the airport.

"There are many dead," an Associated Press television reporter at the scene reported police radio as saying. "The pilot and co-pilot are dead. At least one Frenchman is alive," he reported the radio as saying.

Police said the five hijackers were killed in the assault.

The plane flew to Marignane airport, 25 miles northwest of Marseille, early Monday after a 40-hour standoff in Algiers.

Sixty-five passengers had been freed since the gunmen commandeered the Airbus A-300 Saturday morning in Algeria. Three passengers - a Frenchman, a Vietnamese and an Algerian policemen - were killed while the jetliner stood on the tarmac at Algiers.

A total of 170 passengers and crew were thought to still be on board when the rescue attempt began. About 40 of the passengers and crew were believed to be French, the rest Algerian.

The hijackers, armed with at least two Kalashnikov assault rifles and two automatic pistols, seized the plane Saturday as it prepared to leave for Paris.

Algerian officials said one of the hijackers was a member of the Armed Islamic Group, the most radical Muslim faction in Algeria.

The group has claimed responsibility for the deaths of most of the 71 foreigners killed in the past 15 months as radicals tried to scare off the foreign technical expertise the Algerian government needs to run its oil and other industries. France, which once ruled Algeria, has been the extremists' chief target, and 23 French citizens have been killed.

More than 11,000 people have died in the insurgency, which began in January 1992 when the army-installed government canceled the second round of parliamentary elections to stop Islamic fundamentalists from winning. Monday was the third anniversary of those elections.

The Islamic Salvation Front issued a statement from its office in Germany that said it "denounces and condemns this hostage-taking, those who ordered it, its authors and their demands."

It wasn't clear what the five hijackers wanted. A news report said they had demanded freedom for two jailed Muslim leaders. But an Algerian Interior Ministry official said Sunday they had dropped that demand.