The 51-year-old Kashmir dispute, over which India and Pakistan have fought two of their three wars since independence, has been revived.
Along with the nuclear arms race between the two neighbours, the disputed Himalayan state has been discussed by the five permanent UN Security Council members at their meeting in Geneva.
Kashmir's importance was underlined by the Pakistani foreign minister, Mr Gohar Ayub Khan, after the two sides conducted nuclear tests last month saying Islamabad would not sign the "no-first-use " pact on nuclear weapons offered by India until negotiations on the region began.
"Kashmir is the root cause of the tension between India and Pakistan but the international community has ignored it all along," he said.
Mr Khan insisted that Kashmir, over whose borders Indian and Pakistani troops exchange small arms and artillery fire almost daily, could not be settled without "third-party mediation"; both countries had never settled anything on a bilateral level.
India, on the other hand, is totally opposed to internationalising the Kashmir dispute, preferring to settle it bilaterally.
In 1948, India promised, but never held, a UN-sponsored plebiscite on Kashmir, its only Muslim-majority state. The Indian army stopped Pathan raiders from Pakistan's North West Frontier Province occupying the entire state then ruled by a Hindu king.
Once the Pathans reached the outskirts of Kashmir's summer capital, Srinagar, the Maharaja panicked and acceded to India after which Indian troops halted the raiders' advance.
The Pathan raiders - who occupied a third of Kashmir which Pakistan holds - were violating the six-month "stand still" period agreed upon by India and Pakistan to give the Maharaja time to merge his state with either country or remain independent.
In a separate agreement with China two decades ago, Pakistan handed over around 5,000 square miles of Kashmir. China is reported to have agreed that the territory it was "acquiring" would be subject to the final settlement of the Kashmir dispute and built a military highway across it.
But India says the UN-supervised vote to decide Kashmir's future has been upstaged by subsequent treaties, a claim rejected by Pakistan.
Besides, the UN resolution required the Indian and Pakistani armies to withdraw from Kashmir before any plebiscite was held. "With China now occupying a portion of Kashmir, Pakistan's demand for a plebiscite becomes even more distant," said a security official.
Revived peace talks between India and Pakistan were abandoned last year despite both sides having established working groups to resolve all outstanding issues. A "hot line" between the two prime ministers has not been used since.
The director generals of military operations (DGMO) in India and Pakistan have also a hot line which is used whenever cross-border firing over the disputed line of control intensifies.
"Mutual antagonism, differences over Kashmir and now the nuclear issue makes negotiations difficult, if not impossible," said a diplomat in Delhi. He said Kashmir in particular defied any resolution as neither side was in a position to relinquish control over it.
He said the only possible solution for Kashmir, where armed separatists have been fighting for an Islamic homeland since 1989, was to demarcate the existing line of control as the international border.
Nearly 20,000 people have died since 1989 in Kashmir's civil war which India accuses Pakistan of sponsoring. Pakistan denies the allegation but supports a demand for a UN-supervised plebiscite on Kashmir's self-determination.
A second, indecisive war over Kashmir in 1965 was followed by the third India-Pakistan war which led to East Pakistan breaking away to become Bangladesh. The two sides signed the Shimla Agreement in 1972 agreeing to discuss the Kashmir issue bilaterally, burying for the moment the UN plebiscite option.
Meanwhile, Kashmir's autonomous status under the Indian constitution was eroded by successive corrupt state governments and federal interference, leading to resentment and armed rebellion nine years ago.
Nearly 100,000 Indian paramilitary and military personnel claim to have contained, but not ended, militancy in Kashmir.
Islamabad said yesterday the UN Security Council's critical resolution on India and Pakistan's nuclear tests failed to deal properly with the core issue of Kashmir.
"We regret the council's failure to incorporate the predominant view of its members and the international community, which urgently desires that this root cause of the tension in a nuclearised south Asia should be substantively addressed and a just settlement of the Kashmir dispute expeditiously realised," a foreign ministry spokesman said.
He said the resolution, which condemned both countries for carrying out nuclear tests last month, did not deal effectively with the issues dividing the two.
The Pakistani government hopes for an initiative on Kashmir.
However, there has been little sign that the world community wants to get involved beyond backing UN resolutions calling for a plebiscite and a negotiated settlement.