At least 78 people have been killed in heavy fighting between the Taliban and security forces in the Afghan province of Nuristan, officials say.
Provincial Governor Jamaludin Badar told the BBC that 33 border police had been killed in two days of clashes.
He said 40 insurgents and five civilians had also died after more than 150 heavily armed insurgents attacked from bases in Chitral in Pakistan.
Cross-border attacks are fuelling tensions between the neighbours.
The governments accuse one another of failing to contain the militants. Afghanistan also accuses Pakistan of launching hundreds of rockets into its territory.
Earlier on Wednesday, police in north-west Pakistan said that a group of more than 200 militants crossed the border from Afghanistan and attacked villages in Upper Dir in Khyber Pakhtunkhwa province. The insurgents burned down a school and clashed with villagers.
Correspondents say it is difficult to corroborate the claims of either side, but it is not disputed that the militants have expanded their control in Nuristan in recent months and control the main road to the provincial capital. Strongholds
According to intelligence officials in Nuristan, insurgents attacked border police checkpoints using heavy machine guns and rocket propelled grenades, in the district of Kamdesh.
The BBC's Bilal Sarwary in Kabul says that area of the border has seen a heavy presence of Taliban and al-Qaeda fighters in recent months. US forces withdrew from the area earlier this year.
Two senior security officials in Nuristan told the BBC that fighting started when Pakistani and Chechen insurgents crossed the border from Pakistan to attack police checkpoints.
Nato says that it has provided close air support on Tuesday night after the police observation posts came under attack.
"Our helicopters engaged the insurgents. But this is an Afghan-led operation and our forces are there to assist them,'' Captain Justin Brockhoff told the BBC.
The Taliban deny the attack was launched from Pakistan, insisting that the raid was carried out by militants based in Afghanistan.
Governor Badar said dozens of police were still missing and casualty numbers could rise.
"Our forces fought to the last bullet," he said.
"Some of the posts are high in the mountains and it is very difficult to send ammunition, water and food there."
Police say they are looking for 20 officers who either made a tactical withdrawal or were taken hostage.
Our correspondent says mountainous Nuristan, with its poor communications, has not been a traditional stronghold for the Afghan Taliban. But it does have a history of tribal extremism and militancy.
Officials in Nuristan say they have repeatedly warned of the worsening security situation. They accuse the government and Nato of failing to act, claims the authorities reject.
On Tuesday, outgoing Nato commander Gen David Petraeus said the focus of the war was shifting from Taliban strongholds in southern Afghanistan to the eastern border with Pakistan.
Provincial Governor Jamaludin Badar told the BBC that 33 border police had been killed in two days of clashes.
He said 40 insurgents and five civilians had also died after more than 150 heavily armed insurgents attacked from bases in Chitral in Pakistan.
Cross-border attacks are fuelling tensions between the neighbours.
The governments accuse one another of failing to contain the militants. Afghanistan also accuses Pakistan of launching hundreds of rockets into its territory.
Earlier on Wednesday, police in north-west Pakistan said that a group of more than 200 militants crossed the border from Afghanistan and attacked villages in Upper Dir in Khyber Pakhtunkhwa province. The insurgents burned down a school and clashed with villagers.
Correspondents say it is difficult to corroborate the claims of either side, but it is not disputed that the militants have expanded their control in Nuristan in recent months and control the main road to the provincial capital. Strongholds
According to intelligence officials in Nuristan, insurgents attacked border police checkpoints using heavy machine guns and rocket propelled grenades, in the district of Kamdesh.
The BBC's Bilal Sarwary in Kabul says that area of the border has seen a heavy presence of Taliban and al-Qaeda fighters in recent months. US forces withdrew from the area earlier this year.
Two senior security officials in Nuristan told the BBC that fighting started when Pakistani and Chechen insurgents crossed the border from Pakistan to attack police checkpoints.
Nato says that it has provided close air support on Tuesday night after the police observation posts came under attack.
"Our helicopters engaged the insurgents. But this is an Afghan-led operation and our forces are there to assist them,'' Captain Justin Brockhoff told the BBC.
The Taliban deny the attack was launched from Pakistan, insisting that the raid was carried out by militants based in Afghanistan.
Governor Badar said dozens of police were still missing and casualty numbers could rise.
"Our forces fought to the last bullet," he said.
"Some of the posts are high in the mountains and it is very difficult to send ammunition, water and food there."
Police say they are looking for 20 officers who either made a tactical withdrawal or were taken hostage.
Our correspondent says mountainous Nuristan, with its poor communications, has not been a traditional stronghold for the Afghan Taliban. But it does have a history of tribal extremism and militancy.
Officials in Nuristan say they have repeatedly warned of the worsening security situation. They accuse the government and Nato of failing to act, claims the authorities reject.
On Tuesday, outgoing Nato commander Gen David Petraeus said the focus of the war was shifting from Taliban strongholds in southern Afghanistan to the eastern border with Pakistan.