Pakistan is one of China's closest partners in the region, but Beijing also calls itself a "friendly neighbour" of Afghanistan.

Foreign ministry spokeswoman Mao Ning said China was "deeply concerned about the escalation of the conflict", after Pakistan bombed major cities in Afghanistan including the capital Kabul on Friday.

China "calls on both sides to remain calm and exercise restraint... achieve a ceasefire as soon as possible, and avoid further bloodshed", she told a regular press briefing.

"China has consistently mediated the conflict between Pakistan and Afghanistan through its own channels and is willing to continue playing a constructive role in easing tensions."

The ministry and China's embassies in Pakistan and Afghanistan were "working with relevant parties in both countries on this matter", she said.

Pakistan's latest operation came after Afghan forces attacked Pakistani border troops on Thursday night over earlier air strikes by Islamabad.

Islamabad's defence minister has declared the neighbours at "open war".

China has poured tens of billions of dollars into Pakistan to fund massive transport, energy and infrastructure projects -- part of Beijing's transnational Belt and Road scheme.

Islamabad used Chinese-made military hardware, including jets, against India during a short conflict last May.

But analysts say Beijing has also become a crucial partner of the Taliban authorities since they swept back to power in 2021 after ousting the foreign-backed government.

China has requested both countries ensure the safety of Chinese citizens, projects and institutions, Mao said Friday.

She said Beijing was closely monitoring the situation and would provide assistance to any of its citizens in need.