An Indian missile attack on Pakistani-controlled territory has killed eight people, Pakistan officials have said.
A Pakistan military spokesman has told Reuters that his country's air defences have shot down five Indian planes in retaliation.
He added there had been exchanges of fire with Indian troops at multiple places along the ceasefire line in Kashmir.
Locations in Pakistan-administered Kashmir and in the country's eastern Punjab province were hit in the Indian missile attack, according to Pakistani officials.
Pakistan's information minister Attaullah Tarar told Sky News' The World With Yalda Hakim that his country would do all it could to defend its territory - as tensions escalate even further between the nuclear-armed neighbours.
India said it had carried out a "precision strike" on "terrorist camps" and its actions were "focused, measured and non-escalatory in nature", adding: "No Pakistani military facilities have been targeted."
It said a total of nine sites were targeted and the action by its armed forces was a response to a militant gun attack in Indian-controlled Kashmir last month, which killed 26 people, mostly Indian tourists.
But Pakistan's defence minister Khawaja Asif said all the areas hit early on Wednesday morning local time were civilian places, not militant camps.
At least three areas were hit and one of the missiles struck a mosque in the city of Bahawalpur in Punjab, where a child was killed, and a woman and a man were injured, it was reported.
Also, two women were wounded, one of them critically, in Indian-administered Kashmir in shelling by Pakistani troops, according to Indian police.
'Act of war'
Pakistan's Prime Minister Muhammad Shehbaz Sharif called the Indian missile attack an "act of war" and vowed his country "has every right to give a full and strong response".
The Indian defence ministry said it had launched Operation Sindoor, hitting "terrorist infrastructure" in Pakistan and Pakistan-occupied Jammu and Kashmir "from where terrorist attacks against India have been planned and directed".
The ministry added: "These steps come in the wake of the barbaric Pahalgam terrorist attack in which 25 Indians and one Nepali citizen were murdered. We are living up to the commitment that those responsible for this attack will be held accountable."
Gun attack sparked latest tensions
Tensions between the two countries have been escalating following the gun attack near Pahalgam in the Indian-controlled part of Kashmir last month.
Following the Indian missile attack, Pakistani officials said their country had launched retaliatory strikes.
Pakistani army spokesman, Lieutenant General Ahmad Sharif, told ARY News that the missiles were launched from within Indian territory and that no Indian aircraft had entered Pakistani airspace.
"This was a cowardly attack targeting innocent civilians under the cover of darkness," he told the broadcaster.
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A statement by Pakistani PM Muhammad Shehbaz Sharif said: "The deceitful enemy has carried out cowardly attacks at five locations in Pakistan.
"Pakistan has every right to give a full and strong response to this act of war imposed by India - and a full response is being given. The entire nation stands with the Armed Forces of Pakistan, and the morale and spirit of the Pakistani people are high.
"The Pakistani nation and the Armed Forces of Pakistan know well how to deal with the enemy. We will never allow the enemy to succeed in its nefarious objectives."
Explosions heard
Multiple loud explosions were heard in several places in Pakistan and in the mountains around the city of Muzaffarabad, capital of Pakistani Kashmir.
After the blasts, power was blacked out in Muzaffarabad, witnesses said.
Calls for restraint
UN secretary-general Antonio Guterres is very concerned about Indian military operations in Pakistan and Pakistan-administered Kashmir, according to his spokesperson.
And Mr Guterres has called for maximum military restraint from India and Pakistan.
"The world cannot afford a military confrontation between India and Pakistan," said the spokesperson.
Donald Trump said he hopes the fighting "ends very quickly".
The US president said: "I guess people knew something was going to happen based on a little bit of the past. They've been fighting for a long time. They've been fighting for many, many decades."
Some 26 people were shot dead by gunmen at a beauty spot near the resort town of Pahalgam on 22 April.
India described the massacre as a "terror attack" and said it had "cross-border" links, blaming Pakistan for backing it.
Pakistan denied any connection to the atrocity, which was claimed by a previously unknown militant group called the Kashmir Resistance.
Since the attack, Pakistan's military has been on high alert after a cabinet minister said Islamabad had credible intelligence indicating that India could attack.
And Pakistan's defence minister Mr Asif told Sky's Yalda Hakim that the world should be "worried" about the prospect of a full-scale conflict involving the two nations.
(c) Sky News 2025: Pakistan 'shoots down' Indian jets - after India fires missiles on 'terrorist camps'