Pakistani Prime Minister Imran Khan has vowed to use "every forum" to force New Delhi to reverse its decision to strip Indian-administered Kashmir of its special status and split the Himalayan state.
Addressing a joint session of parliament on August 6, Khan pledged to raise the matter with heads of state and take the issue to the UN Security Council and the International Criminal Court.
He told lawmakers in Islamabad that India's actions, which he called illegal under international law, could lead to an all-out conflict between the two nuclear-armed neighbors, adding, "No one will be the winner in that case."
Earlier, Pakistan's army chief, General Qamar Bajwa, said the military would "go to any extent" to support the people of Kashmir in their "just struggle."
There is a long-running insurgency in Indian-administered part of Kashmir, which is divided between the two neighbors.
The Muslim-majority region is claimed in its entirety by both India and Pakistan.
Two of the three wars the two countries have fought since their 1947 independence from British rule were over Kashmir.
The Indian side of Kashmir remained locked down on August 6 as India's lower house of parliament approved the revocation of Kashmir's special constitutional status that gave it significant autonomy from the rest of the country.
The chamber also cleared a bill to split the Indian state of Jammu and Kashmir into two union territories, a day after the upper house backed the measures.
The Chinese Foreign Ministry said India's decisions were "unacceptable" and that New Delhi needed to be cautious on border issues, drawing a rebuke from the Indian government that the status of Jammu and Kashmir was an "internal matter."
The U.S. State Department earlier expressed concern "about reports of detentions" and urged "respect for individual rights and discussion with those in affected communities."
It called on "all parties to maintain peace and stability along the Line of Control" that serves as a de facto border between India and Pakistan in Kashmir.
Amid fears of fresh violence in the Indian-ruled part of Kashmir, India's moves were accompanied by a telecoms blackout in the region, restrictions on public movement, and the deployment of thousands of troops.
Despite the measures, sporadic protests were reported.
Protests also continued in Pakistani-administered Kashmir and Pakistan for a second day, with hundreds of people shouting anti-Indian slogans.
Meanwhile, Pakistan and India's fierce cricket rivalry spilled over into politics as former stars from the two countries traded barbs over New Delhi's decision.
"Kashmiris must be given their due rights as per #UN resolution. The rights of Freedom like all of us," Pakistan's Shahid Afridi, who announced his retirement from international cricket last year, tweeted.
"Why was @UN created & why is it sleeping? The unprovoked aggression & crimes being committed in Kashmir against #Humanity must be noted. [U.S. President Donald Trump] must play his role to mediate."
Indian Gautam Gambhir, who quit cricket in December and is now a member of parliament for Prime Minister Narenda Modi's party, later took a swipe at Afridi on Twitter, writing: "There is 'unprovoked aggression,' there r 'crimes against humanity'."
Afridi should be "lauded for bringing this up," he said. "Only thing is he forgot to mention that all this is happening in 'Pakistan Occupied Kashmir.' Don't worry, will sort it out son!!!"