India's Prime Minister Atal Bihari Vajpayee today called on the international community to declare Pakistan a "terrorist state," alleging that its role in "fomenting terrorism" such as the hijacking of an Indian Airlines jet "is now too obvious to be any longer overlooked by the world."

Pakistani officials, in turn, denounced India's accusations that the five hijackers were Pakistani nationals who had been allowed to escape into Pakistan. The week-long hijacking drama ended New Year's Eve after India agreed to release three imprisoned Kashmiri Muslim activists for 155 hostages stranded in southern Afghanistan.

"We have repeatedly denounced this terrorist crime, and if any of the hijackers surface in Pakistan they will be immediately arrested and tried in accordance with international civil aviation conventions," Foreign Minister Abdus Sattar said in an interview. "We have no idea who these people are, but it is our responsibility as a state to punish such criminals."

Indian authorities said Sunday they had "clear evidence" that Pakistan was involved in the hijacking, and that the hijackers, who were allowed to go free after releasing the hostages, had escaped into Pakistan. They said they have proof that the hijackers spoke by radio with "their mentors" in Pakistan during the hijacking.

The unidentified hijackers claimed to be supporters of the Islamic separatist insurgency that opposes Indian control of southern Kashmir, a disputed region that is divided between India and Pakistan. The insurgency has long been backed by Pakistan, and the three prisoners were prominent in the Kashmiri rebel movement.

Afghan authorities have said the hijackers and freed prisoners left Afghanistan. It is widely believed that they crossed the porous border into Pakistan and vanished, although Pakistani officials said they had mounted extra security measures at border crossings.

"Our border authorities have been ordered to be vigilant for suspicious persons, and no one has come to their notice," Sattar said. "But no one knows what these people look like, so it is like looking for a needle in a haystack. Given the lack of information, any claim can be made."

India and Pakistan, longtime adversaries whose most bitter dispute is over Kashmir, have hurled accusations at each other since the hijacking drama began Dec. 24. Even after the successful negotiations that led to the hostages' release, the two governments have attempted to implicate each other in the crime.

While India has charged that the hijackers were taking instructions from inside Pakistan, officials in Islamabad have raised their own questions about India's role in the events. They have asked why India allowed the commandeered plane to land and take off from Amritsar, India, and suggested that New Delhi sought to lump Pakistan with terrorists.

In Washington, State Department spokesman James P. Rubin said the United States does not know where the hijackers have gone but said Pakistan had pledged "that it will meet its obligations under the international conventions to apprehend the hijackers and bring them to justice."

In Kashmir today, there was heavy shelling, and 17 people were killed by a land mine in a market outside the city of Srinagar on the Indian-controlled side. No one claimed responsibility for the explosion. And in Pakistani-held Kashmir, five civilians were killed by repeated Indian shelling, Pakistani officials said.

The hijacking crisis has forced Indian and Pakistani authorities to play a delicate domestic balancing act. The Indian government was eager to placate the hostages' families by obtaining their relatives' safe release, but it has been strongly criticized by the armed forces--and even by some hostages--for giving in to terrorist demands.

Pakistan, while formally denouncing the hijacking, is also reluctant to alienate Kashmiri insurgent groups because their cause is sacred to many Pakistanis and has long been sponsored by the Pakistani armed forces. Many people have suggested that the hijackers and released prisoners will head for Pakistani Kashmir, and the governor of that state has said he will consider a request from the hijackers if they seek to enter the area.

On the other hand, several major Islamic insurgent groups fighting in Indian Kashmir have condemned the hijacking, saying they do not support terrorist acts against civilians and suggesting that such a crime will boomerang against their crusade to liberate Kashmir and spread Islam.

"We think this will damage our cause," said Abdullah Muntazir, information secretary for the Lashkar-e-Taiba insurgent group in Islamabad. "Islam condemns such acts against innocent women and children, and this will only give India a chance to make propaganda against Islam and the jihad," or Islamic holy war.

Another insurgent umbrella group here, the United Jihad Council, said that Kashmiri insurgents "were not involved in the hijacking drama, and we are of the view that such actions are against humanity." A spokesman, who uses the name Kalim, said today that "our only target are the Indian forces that occupy our land."

The hijackers, however, appear to be affiliated with a third insurgent group, the Harkat ul-Mujaheddin, which has repeatedly targeted civilians, including foreign tourists and Indian religious pilgrims, for attack. Efforts to reach spokesmen for that group today were unsuccessful.

The freed prisoners were members of that insurgent group or its affiliates. One of them, Maulana Masood Azhar, was a spiritual ideologue for a related religious group. The second, Mushtaq Ahmad Zargar, was arrested with Azhar in 1994 and charged with murder. The third, Omar Sheikh, was arrested in 1996 in a plot to kidnap foreign tourists in New Delhi.

The most spectacular and gruesome crime attributed to Harkat ul-Mujaheddin and its affiliate, Al Faran, was the 1995 kidnapping of six Western tourists who were hiking in Indian Kashmir. One, a Norwegian, was beheaded. The others, a German, two Britons and one American, have never been found. A second American escaped. The kidnappers demanded the release of Azhar and two other activists, but India refused to comply.

All major political opposition groups in Indian Kashmir have condemned the hijacking, but Indian authorities said Sunday they had intercepted radio conversations suggesting that these groups had made the denunciations only on orders from inside Pakistan.

While accusations continued to fly between India and Pakistan, there were also signs that the new-found spirit of cooperation between Indian and Afghan authorities that led to the hostages' release is beginning to fray. On Saturday, Indian officials said Afghan officials had told them the hijackers had left Afghanistan and entered Pakistan, but on Sunday the Afghans denied having made such a statement.

Staff writer Steven Mufson in Washington contributed to this report.