A mysterious chemical fire in a seedy Philippine hotel in January 1995 foiled the first plot to blow American airliners out of the sky with liquid bombs _ a grisly scenario allegedly planned by extremists arrested in Britain.

British authorities said Thursday they had thwarted a terrorist plot to simultaneously blow up 10 aircraft heading to the U.S. using explosives smuggled in hand luggage in a plan that police described as"mass murder on an unimaginable scale."

The alleged plot was grimly reminiscent of a plan developed in late 1994 and early 1995 by Ramzi Yousef, who is serving a life sentence without parole in the United States for masterminding the bombing of the World Trade Center in 1993.

Yousef planned to blow up a dozen U.S. airliners over the Pacific and even carried out a test bombing in December 1994, smuggling nitroglycerine onto aPhilippine Airlines jet in a contact lens solution bottle.

The explosive detonated near Okinawa, killing a Japanese man after Yousef had gotten off the plane in Cebu, Philippines. The plane managed to land safely in Okinawa.

At the time, however, authorities had no idea of the link between the blast and Yousef. That would come later after an intensive investigation of the strange events that unfolded on the night of Jan. 6, 1995, in Suite 603 of the Dona Josefa apartment-hotel, located near Manila's raucous red-light district.

A month before, two Middle Eastern men had checked into the hotel, which offered low-cost, long-term accomodations. It was about 200 yards (182 meters) down the street from the residence of the Vatican envoy _ where Pope John Paul II was to stay while attending the World Youth Day festivities the following month.

One of the men registered as Naji Haddad and listed his nationality as Moroccan. Police later determined that Haddad was Ramzi Yousef. His companion was Abdul-Hakim Murad, a Pakistani who grew up in Kuwait.

The new tenants immediately attracted suspicion.

Hotel staff noticed a series of Middle Eastern-looking men shuttling in and out of the apartment, often bringing boxes and metal pipes. Manila had been rocked by a series of small explosions in recent weeks, and the local press was full of warnings about extremists within the country's Muslim minority.

The neighborhood watch association reported the suspicious activity to the police, who advised they had no legal grounds to search the room. But police were concerned about security for the upcoming papal visit and advised the hotel staff to keep a close watch on Suite 603.

On the night of Jan. 6, six days before the pope was to arrive, security guard Roman Mariano saw Yousef and Murad, whom the hotel knew as Ahmed Saeed, running down the stairs."They seemed upset,"Mariano said.

Moments later, a security guard reported smoke billowing from Suite 603.

Firemen were summoned and the room filled with acrid fumes. Yousef had disappeared in the confusion but Murad explained they were just fireworks for a delayed New Years'Eve celebration.

Firemen left but the police returned later and searched the apartment thoroughly. They found explosives, wires, Bibles, pictures of the pope and maps of the papal route. Police staked out the apartment and were waiting when Murad returned about 2 a.m.

Under intensive interrogration over time, Murad gave up a plot _ to kill the pope and blow up American planes. Corraborating evidence was found on a laptop and diskettes found in Suite 603.

Three days after Murad's arrest, the U.S. Federal Aviation Administration issued a security alert for all American airliners flying over the Pacific, including a ban on hand-carried liquids, aerosols and shaving cream.

Yousef slipped out of the country and made his way to Pakistan, where he was arrested a month later and sent to the United States. Murad was extradited to the United States the following April and testified against Yousef.

Both are serving sentences of life without parole at the Florence Super-Max federal prison in Colorado.

Robert H. Reid, correspondent-at-large for The Associated Press, was chief of bureau in Manila in January 1995.

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