Islamic extremists who hijacked an Air France flight in Algiers planned to blow up the plane and its 171 occupants over Paris, former hostages said Tuesday.

In Algeria, four Catholic priests, including three Frenchmen, were shot to death Tuesday in Tizi-Ouzu, 60 miles east of Algiers. The gunmen escaped, and there was no claim of responsibility and no indication if it was related to the hijacking.French investigators discovered 20 sticks of dynamite rigged with detonators hidden under two seats in the plane, which French commandos stormed in Marseille on Monday. The four hijackers were killed, but all the hostages survived.

The hijackers asked to have 27 tons of kerosene loaded into the plane's gas tanks, whereas only 10 tons is necessary to make the trip to Paris, regional Gov. Hubert Blanc said Monday.

The extra kerosene, which jets use as fuel, would have caused a bigger explosion if the plane did blow up.

"Their idea was to set Paris ablaze," Ferhat Mehenni, a well-known singer in Algeria, told TF-1 TV. "They whispered it among themselves, and passengers overheard them."

The dynamite was found under a seat just behind the Airbus A300's cockpit and under another seat in the jet's midsection, Marseille Police Chief Alain Gehin said.

The plane was low on fuel when the hijackers ordered it flown from Algiers to Marseille. There, they demanded that it be refueled for a flight to Paris.

Gehin said he never heard the hijackers express an intent to detonate the explosives in midair.

"Throughout our dialogue, it was understood that I could not take the risk of allowing a plane to take off that could be susceptible to being blown up in the air," Gehin said.

The hijackers had demanded to be flown to Paris by 5 p.m. Monday or they would kill a fourth hostage. Three were slain in Algiers.

When the deadline passed and authorities were still trying to negotiate, the hijackers fired gunshots at the airport's control tower, shattering a window and apparently provoking the raid.

The commandos burst into the plane firing guns and stun grenades. The exchange of gunfire lasted about four minutes.

The assault "was very quick," an unidentified Algerian woman told Europe-1 radio. "I saw the commandos coming on the stairways. I hid under my chair. I told my daughter, who was sitting in front of me with her daughter, to get under their seats, too.

"Then we saw people with helmets," she said. "They told us not to move. Then they said, `Quick, get out quick. Jump out and run, but stay bent over, above all don't stand up.' "

Co-pilot Jean-Paul Borderie clambered out a cockpit window and fell to the tarmac. He got up, clutching one arm, and hobbled away.

Thirteen passengers, three crew members and nine commandos were injured. One rescuer had three fingers blown off by a concussion grenade, but doctors said one finger was reattached and he would regain use of his hand.

The hijacking was the first time Algeria's 3-year-old civil war spilled violently onto the soil of France, its former colonizer. Islamic extremists have increasingly targeted foreigners in their campaign to topple Algeria's military-backed government.

The news agency Agence France-Presse said it received a claim of responsibility Monday from the Armed Islamic Group's "Phalange of the Signers in Blood." It said the action was a response to France's "unconditional aid" to the Algerian regime.

The rescue was seen as one of the most successful anti-terrorist operations in aviation history. The commandos were lauded as national heroes, and President Francois Mitterrand expressed "the nation's gratitude."

"We expected death. We were waiting for the explosion," Ali Kalak, a passenger, told Associated Press Television Tuesday. "We never thought there would be such a successful intervention."

The gunmen seized the Paris-bound jet at the Algiers airport on Saturday, demanding the release of jailed fundamentalist leaders. The plane flew to Marseille early Monday after 63 passengers were released and three were killed.

Two more passengers were freed in Marseille, but passengers feared more killings there.

"They had said a few prayers, especially prayers for people preparing to die," the unidentified Algerian woman told Europe-1 radio. "At the moment when the commandos attacked, they shouted, `We'll show the French what we're capable of doing."

Cheers, tears and joyful chaos greeted nearly 80 former hostages as they arrived Tuesday at Paris' Orly Airport. The commandos got the loudest applause.

Several of the hostages said they had been well-treated despite the terror. "They were very correct with us," said an Algerian who identified himself only as Ahmed. "We talked normally with them."