Pakistan's strikes on Friday hit Taliban military installations and posts, including in Kabul and Kandahar, in one of the deepest Pakistani incursions into its western neighbour in years, officials said.
Islamabad accuses the Taliban of harbouring Tehreek-e-Taliban Pakistan (TTP) militants, who it claims are waging an insurgency inside Pakistan, a charge the Taliban denies.
Pakistan described its actions as a response to cross-border assaults, while Kabul denounced them as a breach of its sovereignty, saying it remained open to dialogue but warned any wider conflict would result in serious consequences.
The fighting has raised the risk of a protracted conflict along the rugged 2600km frontier.
Diplomatic efforts gathered pace late on Friday as Afghanistan said its foreign minister, Amir Khan Muttaqi, spoke by telephone with Saudi Arabia's Prince Faisal bin Farhan about reducing tensions and keeping diplomatic channels open.
The European Union called for both sides to de-escalate and engage in dialogue, while the United Nations urged an immediate end to hostilities.
Russia urged both sides to halt the clashes and return to talks, while China said it was deeply concerned and ready to help ease tensions.
The United States supports Pakistan's right to defend itself against attacks by the Taliban, a State Department spokesperson said.
A US official, speaking on condition of anonymity, said Washington did not view Pakistan as the aggressor in the latest escalation and that Islamabad was under pressure to address its security challenges, adding Washington hoped the situation would not escalate further.
Exchanges of fire continued along the border overnight into Saturday.
Pakistani security sources said an operation dubbed "Ghazab Lil Haq" was ongoing and Pakistani forces had destroyed multiple Taliban posts and camps in several sectors.
Both sides have reported heavy losses with conflicting tolls. Pakistan said 12 of its soldiers and 274 Taliban were killed while the Taliban said 13 of its fighters and 55 Pakistani soldiers died.
Taliban deputy spokesman Hamdullah Fitrat said 19 civilians were killed and 26 wounded in Khost and Paktika.
Pakistan's Defence Minister Khawaja Muhammad Asif said "our cup of patience has overflowed" and described the fighting as "open war", warning that Pakistan would respond to further attacks.
Taliban Interior Minister Sirajuddin Haqqani said in a speech in Khost province that the conflict "will be very costly," and Afghan forces had not deployed broadly beyond those already engaged.
He said the Taliban had defeated "the world, not through technology, but through unity and solidarity," and through "great patience and perseverance," rather than superior military power.
Pakistan's military capabilities far exceed those of Afghanistan, with a standing army of hundreds of thousands and a modern air force.
In stark contrast, the Taliban lacks a conventional air force and relies largely on light weaponry and ground forces.
However, the Islamist group is battle-hardened after two decades of insurgency against US-led forces before returning to power in 2021.
