Hijackers of an Indian Airlines jet that landed today in Afghanistan have demanded the release of an anti-Indian Islamic leader and several other militants jailed in the restive Indian state of Kashmir, threatening to kill the 161 passengers and crew on board unless discussions begin.

The demands provided the first clear indication of what motivated the five heavily armed men who took over the Airbus A300 on Friday as it was en route from Katmandu, Nepal, to New Delhi, diverting it to stops in India, Pakistan and Dubai before the landing early this morning at Kandahar in southern Afghanistan.

"The hijackers have broken their silence," declared Ravindra Gupta, India's civil aviation secretary. "The matter of negotiations is attracting our attention."

The man whose release they demanded, Maulana Mansood Azhar, is a Pakistani and a leader of the Harkat ul-Mujahedeen movement, which is agitating to split Kashmir from India. Azhar was jailed in 1994, and Islamic allies have tried three previous times since then to force his release.

According to reports from India, one of the hijackers is thought to be Azhar's brother, Ibrahim. A passenger who was among 25 released when the plane refueled in Dubai, in the United Arab Emirates, said on his return to India today that the group includes three Kashmiris, one Afghan and one Nepali.

Afghanistan's ruling Taliban regime has refused to negotiate with the hijackers, insisting that the United Nations intervene. "We have told the United Nations if they do not take immediate action in this regard, we will order the airplane to leave Afghanistan to go to another place," the Taliban representative to the United Nations, Maulvi Hakim Mujahid, told India's Star News in a telephone interview. "The situation is so, so serious, we are afraid not to have any kind of catastrophe there."

In New York, U.N. spokeswoman Nina Wehmer said U.N. envoy Erik de Mul is monitoring the situation closely from Pakistan, but she said the world body has received no formal request to become involved. "The U.N. stands ready to help in any way it can," she added.

India, meanwhile, prepared to send negotiators to Afghanistan to work with the United Nations if there are negotiations. "The Indian government's priority is to safeguard the lives of the passengers and the crew," Chaman Lal Gupta, India's minister of state for civil aviation, told reporters in New Delhi.

Enforcing strict discipline on board, the hijackers have killed at least one man who, according to those released, disobeyed orders to keep their heads between their legs and their eyes closed. The victim was identified today as Rupin Katyal, 25, who was returning with his wife from their honeymoon. They were married on Dec. 3, according to reports from India. Earlier reports, which were not officially confirmed, indicated that as many as four others aboard the plane may have been killed.

As the aircraft sat on the tarmac in Kandahar, Indian officials said they believed Taliban authorities were making food and water available to the passengers and crew. The Indian minister for external affairs, Jaswant Singh, said he felt those on board were "as comfortable as possible given the circumstances."

In New Delhi, Indian Prime Minister Atal Bihari Vajpayee condemned the hijacking and said his government will not capitulate to terrorists. "This is a very cowardly act; India will never be cowed down by such barbaric acts," Vajpayee told reporters, according to news service reports.

Focused as it is on a Kashmiri separatist leader, the incident again highlighted the trouble that continues to plague the Indian subcontinent because of the conflict over the majority Muslim region. Most Indians are Hindus, and controversy over control of Kashmir has sparked intense border skirmishes with the neighboring Muslim state of Pakistan. Azhar is from a well-to-do, landowning family in Pakistan, according to news service reports.

The involvement of the Taliban in Afghanistan complicates matters, because their goal is to create a strict Islamic state in Afghanistan and because they are not recognized by India or most of the rest of the world as a legitimate Afghan government. Some Indian analysts accused the Taliban of training some members of Azhar's movement and said India should not trust Taliban statements disavowing the hijacking and terrorism in general. Taliban officials have refused to grant the five hijackers political asylum and have denounced the plane's seizure.

The Harkat ul-Mujahedeen has proved before that it considers Azhar important enough to kill for. In 1995, the group kidnapped six Western tourists hiking in Kashmir and demanded Azhar's release. When India refused, one tourist was killed. One escaped, and the other four are missing and presumed dead.

Azhar entered India in 1992 to join the anti-Indian movement in Kashmir. He was apprehended by Indian authorities two years later in Anantnag, a village in northern Kashmir.

Correspondent Colum Lynch at the United Nations and special correspondent Debdeep Chakraborty in New Delhi contributed to this report.