India has asked Pakistan to extradite the five hijackers of an Indian Airlines plane so that they can stand trial there.

This is the first official diplomatic demand by Delhi since the hijacking in December.

The Pakistani High Commissioner to India, Ashraf Jehangir, was summoned to the Ministry of External Affairs in Delhi and told that his country had a legal obligation to extradite the hijackers and their accomplices to India.

Islamabad has always denied that the hijackers are in Pakistan, and has demanded that Delhi provide hard evidence for this assertion.

The authorities in Pakistan have said that they will arrest and try the hijackers if they enter the country. Islamabad has also denied India's allegation that it masterminded the hijack.

The hostages' eight-day ordeal ended with the release of all 155 remaining passengers at Kandahar airport in Afghanistan, after India released three Kashmiri militants from prison. One passenger was killed during the hijacking.

The five hijackers have not been seen since they disappeared into the Afghan desert on 31 December following the militants-for-hostages swap.

The Indian External Affairs Ministry said in a statement: "Given that a large number of terrorists whose release was sought by the hijackers are Pakistani nationals and the first destination chosen by the hijackers was Lahore, there were strong grounds for believing that the hijackers were currently in Pakistan."

"The Pakistani High Commissioner was also informed that the Government of India reserved the right to take further measures as appropriate," the ministry said, without elaborating.

The extradition, the statement said, "would be in fulfilment of Pakistan's obligations under international conventions to which it is a signatory".

No formal extradition treaty exists between the two countries.

Hijackers 'were Indian'

A Pakistani cleric who was one of the three militants freed by Delhi earlier this week vowed to continue fighting Indian forces in Kashmir.

Maulana Masood Azhar told a rally at his home town of Bhawalpur in Pakistan that he would recruit half a million men to fight in Indian-administered Kashmir.

The cleric also told a Pakistani newspaper that he believed the hijackers were in Pakistan.

He also said that they were Indian, rather than Pakistani as is widely assumed. He said that the responsibility for the death of one of the passengers lay with Delhi.