A Pakistani air strike on a drug rehabilitation centre in Kabul killed at least 408 people on Monday, according to Afghan officials.
The Taliban-led government said a further 265 people were injured when the strike hit the Omid Addiction Treatment Hospital in the Afghan capital.
Islamabad has rejected the claims of civilian casualties, maintaining that its forces targeted "military installations and terrorist support infrastructure."
A spokesperson for the Pakistani military said the operation was "precisely and carefully undertaken" to avoid collateral damage.
Pakistan has not verified the reported casualty figures in the incident that follows a month of the heaviest fighting between the two nations in years.
Tensions ignited in February when Pakistan launched air strikes inside Afghanistan against what it described as militant strongholds.
Kabul responded by branding the move a violation of its sovereignty and launched retaliatory operations.
Over the last three weeks, both countries have engaged in sustained air and drone strikes alongside ground fire across their 1,600-mile border.
READ ALSO: Israel Claims Assassination of Iran Security Chief, Other
Both sides claim to have killed hundreds of opposing troops, though neither has provided evidence to support these figures.
Islamabad has repeatedly accused the Afghan Taliban of providing safe havens for militants, specifically the Tehreek-e-Taliban Pakistan (TTP), to launch attacks on Pakistani soil.
It further alleges that Afghanistan hosts insurgents seeking independence for the province of Balochistan.
The Taliban administration denies these allegations, insisting that militancy in Pakistan is an internal domestic issue.
Diplomatic efforts to resolve the crisis have so far stalled, while Turkey, Qatar, and Saudi Arabia successfully mediated a ceasefire following border clashes in October with no negotiations during the current escalation.
It was said that despite calls from Russia and Turkey for a return to diplomacy, Islamabad has shown no inclination to negotiate, despite Kabul expressing a willingness to do so last month.
Consequently, China, a strategic ally to both nations, urged "dialogue and negotiation" on Tuesday.
A spokesperson for the Chinese foreign ministry said Beijing would continue to play a "constructive role" in de-escalating the situation.
Tags: #Afghanistan, #Pakistan, #Kabul, #BreakingNews, #HumanitarianCrisis