Hijackers of an Indian Airlines jet threatened to begin killing hostages today if the Indian government does not take what a United Nations representative referred to as "concrete steps" to meet their demanded release of a Pakistani religious leader currently in jail in India.

"The hijackers have threatened they will start killing the passengers if the Indian government does not take concrete steps," Erik de Mul told reporters at the Kandahar airport in Afghanistan after talking with the hijackers and the pilot of the Airbus A300. The plane has been on the ground in Kandahar for two days after it was hijacked by five armed men on Friday while en route from the Nepalese capital of Katmandu to New Delhi.

De Mul, whose visit to the airplane had been described earlier in the day as strictly a "humanitarian" effort to check on the status of 161 passengers and crew, relayed the threat to reporters, and said the hijackers had set a deadline of 8:10 a.m. Greenwich Mean Time--shortly after noon in Afghanistan and 3:10 a.m. EST. De Mul said the pilot had appealed to the world "to do something" or the hijackers would start killing the hostages still aboard after the deadline expires.

De Mul also said that the captain of the plane had appealed to world leaders "to do something," and added that the mental and physical condition of those on board "was bad."

The death threat comes after the hijackers have held the plane for three days, and as the governments of India and Pakistan began feuding over who is responsible for the incident.

India asserted that the hijackers had arrived in Nepal aboard a Pakistani airliner and, with weapons in hand, were able to quickly transfer onto the targeted plane without extra security checks, a charge which Pakistan denied.

Pakistan's foreign minister responded by accusing India of staging the hijacking to malign Pakistan's new military government.

De Mul visited the passengers to verify that they are being fed and to check on their condition. The hijackers released one additional passenger, a diabetic.

However, the hijackers did not comply with pleas to release the widow of a passenger who was stabbed to death on Friday. Under the hijackers' control, the plane wandered through stops in India, Pakistan and the United Arab Emirates before stopping in Kandahar. India had requested that the widow be allowed to attend her husband's funeral today.

The air in the plane "is very bad. . . . It smells like people have been sick," said Mohammed Khiber, a civil aviation authority for Afghanistan's ruling Taliban, who have delivered food to passengers. The plane's engine's were running and the shades remained drawn, said Afghan officials.

The man's stabbing is the only confirmed death, though the hijackers have threatened to kill all on board, and themselves, if the anti-Indian militant Maulana Masood Azhar is not released from a Kashmiri jail, along with others who have been fighting to make Kashmir part of Pakistan. Both India and Pakistan claim Kashmir, which like Pakistan is mostly Muslim. Most Indians are Hindus.

After three days of tension, and amid mounting criticism in India over the government's handling of the hijacking, regional troubles surfaced. Indian External Affairs Minister Jaswant Singh said Pakistan had tried over the years to secure the release of Azhar, suggesting sympathy with the hijackers' cause.

Though India has not yet sent officials to Afghanistan, Singh said the government is in communication with the hijackers "directly via the air traffic control and other authorities in Afghanistan."

The Indian cabinet, caught between the demands of passengers' relatives to release Azhar and security officials' arguments that any concession to the hijackers would encourage terrorism, held emergency meetings. Singh said all possibilities are under discussion.

Afghan politics are also complicating the crisis. The Taliban, who practice a strict form of Islam, are not recognized by most of the world as Afghanistan's legitimate government, and a member of an opposing faction, who still serves as Afghanistan's ambassador to India, charged that the Taliban have orchestrated the hijacking with Pakistan.

Aviation authorities in Kandahar have said the plane has been refueled, but it remains unclear when it will leave or where it might go. Taliban officials acknowledged the plane is leaking oil and may have other mechanical problems, and have said they would not ask the plane to leave until all of the problems are addressed.

Special correspondents Colum Lynch at the United Nations and Debdeep Chakraborty in New Delhi contributed to this report.

CAPTION: An unidentified man walks past the hijacked Indian Airlines jet as it sits on the tarmac at Kandahar, Afghanistan, under the control of five armed men.