In a fiery speech to about 10,000 supporters here today, one of three Islamic insurgents released from prison by India to end an airplane hijacking vowed to fight to liberate Indian-ruled Kashmir and to attack American interests.

Maulana Masood Azhar, who came here from Afghanistan after the eight-day hijack drama ended Friday, told the crowd: "I have come back, and I will not rest in peace until Kashmir is liberated. . . . This is my duty--to tell you that Muslims should not rest in peace until we have destroyed America and India."

Azhar, leader of a radical Kashmiri rebel group called Harkat ul-Mujaheddin, said that the five hijackers who won his freedom in exchange for more than 150 hostages aboard the Indian Airlines plane were all Kashmiris. Speaking over a loudspeaker from inside a simple white mosque, he said the gunmen had returned to Kashmir, a Himalayan region divided between India and Pakistan, where they are "preparing for their next assault."

After days of tense negotiations with the gunmen, India agreed to free Azhar and two other jailed insurgents and flew them to the airport at Kandahar in southern Afghanistan, where the exchange took place. Another freed insurgent, Mushtaq Ahmad Zargar, was greeted by jubilant Kashmiri militants when he arrived Tuesday in the city of Muzaffarabad, in Pakistani-controlled Kashmir.

The whereabouts of the third freed insurgent, Ahmad Omar Sikh, a Pakistani-born British citizen, was not clear. Azhar, a Pakistani cleric, and Sikh had been in Indian jails since 1994, although neither reportedly had been formally charged.

Pakistan said after the hijacking that its border security was put on alert and that the hijackers would be arrested if found--a difficult task given the length and porousness of the Afghan-Pakistani border. Pakistani officials had said, however, that Azhar would be allowed to enter because he did not face any charges here. India and Pakistan have exchanged bitter accusations since the hijack drama ended; India says Pakistan orchestrated the affair, while Pakistan denies the allegation.

The hijackers commandeered the Airbus A300 as it flew from Katmandu, Nepal, to New Delhi on Dec. 24, beginning an odyssey that took it to airfields in northern India, Pakistan and the Persian Gulf region before it finally reached Kandahar. One hostage was fatally stabbed by the hijackers for disobeying an order. After the hostage exchange, the five gunmen were given 10 hours to leave the country by Afghan authorities, and they have not surfaced since.

Meanwhile, police in Indian Kashmir said that a body exhumed there in 1997 is that of a missing British tourist kidnapped along with five others by Azhar's group while trekking in 1995.

"We have received a report of DNA tests . . . confirming that the body was of Paul Wells," said police official Gurbachan Jagat. Authorities are still searching for three missing tourists--Donald Hutchings of Spokane, Wash.; Keith Mangan of Britain and Derk Hasert of Germany. The body of another was found earlier and one of the kidnapped men escaped.