United Nations Secretary-General Antonio Guterres urged India and Pakistan to exercise restraint, his spokesman said on Monday, after India revoked the special status of Kashmir, the Himalayan region that has long been a flashpoint in ties with neighbouring Pakistan.
Monday's move reflects Indian Prime Minister Narendra Modi's muscular approach to national security.
It also is a "promise fulfilled", because Modi's BJP party had scrapped the special status in their electoral manifesto before the 2019 election.
In February, he ordered warplanes into Pakistan after a militant group based there claimed responsibility for a deadly attack on a military convoy in Kashmir.
That prompted a retaliatory raid by Pakistan.
Introduced decades ago, the constitutional provisions reserved government jobs and college places for Kashmir's residents, among other limits aiming to keep people from other parts of India from settling the state.
The government has also decided to split the state into two union territories, one formed by Jammu and Kashmir, and the other consisting of the enclave of Ladakh, citing internal security considerations.
Turning the state into a union territory allows Delhi to exert greater control.
"Today marks the darkest day in Indian democracy," former chief minister Mufti, who remains under house arrest, said on Twitter.
"It will have catastrophic consequences for the subcontinent."
India's interior ministry ordered all states to put security forces on "maximum alert" to maintain public order and quash the spread of any rumours.
BJP general secretary Ram Madhav hailed the government's actions as ushering in a "glorious day".
In Mr Modi's home state of Gujarat, people shouted slogans of support on the streets.
And many Indians have welcomed the move on social media.
In Pakistan, there was anger at India, with protests extending to the capital, Islamabad and the southern commercial centre of Karachi.
In Muzaffarabad, 45km from the two countries' contested border, dozens of protesters held black flags and burnt car tyres, chanting "down with India".
Tension had risen in Kashmir since Friday, when Indian officials issued an alert over possible militant attacks by Pakistan-based groups.
Pakistan rejected those assertions, but thousands of Indians left the region over the weekend.
On Sunday, Pakistan's Prime Minister Imran Khan said the tension had the potential to become a regional crisis and the time was right for US President Donald Trump to mediate.
In July, Mr Trump said Mr Modi had asked him if he would like to be a mediator on Kashmir, but India, which has been staunch in its position that the issue can only be resolved bilaterally, denied that Mr Modi sought mediation.
Kashmir's bloody history: A timeline
In 1947, a secular India and a Muslim-majority Pakistan were created after obtaining independence from British colonial rule.
The ruler of Kashmir, Maharaja Hari Singh did not agree to cede to either country at the time of India's partition in August 1947.
But when Pakistani tribesmen made an incursion into Kashmir in October 1947, Maharaja Hari Singh formally ceded to India.
The first Indo-Pakistani war over Kashmir then took place during 1947-48 and the United Nations intervened. It was decided that a plebiscite would be held. But that has never taken place.
A UN-backed ceasefire line agreed by the two nations in July 1949 became the de-facto frontier.
In 1953, the-then Jammu and Kashmir Prime Minister Sheikh Abdullah was dismissed and imprisoned by New Delhi for almost 11 years because of his support of the region's independence.
Then in 1957, the constitution of Jammu and Kashmir came into force and gave the state a special position in India's union.
For two years in the 1960s, Pakistan launched a war against India for control of Kashmir, which ended inconclusively after a ceasefire brokered by the then Soviet Union.
From 1971-72, a new India-Pakistan war led to the splitting away of East Pakistan, which became the independent state of Bangladesh. Following the conflict, the two nations sign the Simla Agreement and the ceasefire line becomes known as the Line of Control.
In 1975, Prime Minister Sheikh Abdullah returned to power to become the state's first chief minister after partition.
In 1984, Maqbool Bhat, the founder of a leading political separatist group the Jammu Kashmir Liberation Front was hung in a New Delhi jail for murdering an intelligence officer.
Up into the 1990s, a Muslim uprising broke out against Indian rule in Indian Kashmir, inflaming tensions with Pakistan.
Tens of thousands of Kashmiri Hindus, known as Pandits, fled to Hindu-dominated areas of the disputed region and other parts of India in the wake of an armed insurgency.
In 1996, state assembly elections were held for the first time in seven years, but the contentious poll was marred by allegations of coercion by New Delhi.
Infiltrators from Pakistan raided Indian Kashmir's Kargil sector in 1999, sparking a six-week conflict leading to the deaths of 1000 combatants on both sides.
After ending under US pressure, the two nations agreed to a 1999 declaration calling for a negotiated settlement of all issues, including Kashmir.
A new series of attacks in 2001 and 2002 led to a new mobilisation of Indian and Pakistani troops at the de-facto border.
In November 2003, Pakistan declared a unilateral ceasefire along the Line of Control, which led to an inconclusive peace process the following year.
The state government had planned to hand over a plot of land to a trust managing an annual pilgrimage, but that sparked separatist claims of a Hindu takeover and instigated anti-India protests. The transfer was eventually rescinded.
In 2010, a bloody uprising over the death of three civilians saw more than a hundred killed in street protests.
Then in 2016, the killing of a popular rebel leader sparked months of street protests and more than a hundred were killed. Later that year, 18 soldiers were killed after an assault on an army base in Kashmir. India said its special commandos carried out a series of lightning strikes along the border with Pakistan in Kashmir, a claim Pakistan denied.
New Delhi vowed retaliation after at least 40 paramilitaries are killed in a suicide attack in Indian Kashmir earlier this year, which it blamed on a Pakistan-based militant group.
The attack prompted tit-for-tat airstrikes between the two nuclear-armed nations, taking them to the brink of war.
This week, on 5 August, the Indian government revoked Kashmir's special status, stripping it of the significant autonomy it has enjoyed for seven decades.
Tourists stay away
Kashmir (the former state of Jammu and Kashmir) is bordered by China, India, Pakistan and Tibet. It's a region around the size of Germany that features majestic mountain peaks, deep valleys and barren plateaus.
But the instability has thwarted tourism.
In India, the number of visitors dropped from more than 1.3 million in 2012 to 850,000 in 2018, according to government figures.
The Kashmir region has given its name to the soft cashmere wool produced on both sides of the divide that is used to make shawls and scarves that are prized in the West and can fetch high prices.
Among the most expensive is wool from pashmina goats reared by nomads in the Changthang area of Indian Kashmir. Hand-spun into shawls, it is embroidered with typical intricate designs.
Kashmir willow is widely used in the production of the cricket bat.