More than 100 Taliban members crossed over from Afghanistan and attacked three Pakistani military posts Sunday night.
Reports say that anywhere from eight to 13 Pakistani soldiers were killed, and seven were beheaded, according to Reuters. At least 14 militants were also killed in the attacks.
Reuters also reported that the Malakand faction of the Pakistan Taliban claimed responsibility for the attacks, and threatened more.
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"Our fight will continue until the establishment of sharia law in Pakistan ... We will fight whoever tries to stand in our way," Sirajuddin Ahmad, the faction's spokesman, told Reuters.
However, CNN reported that Pakistan Taliban spokesman Ehsanullah Ehsan said the Afghan Taliban carried out the attacks. The news organization also said that three Pakistani military officials confirmed the attack, but asked not to be named, as they are not authorized to speak to the media.
Newly elected Pakistani Prime Minister Raja Pervaiz Ashraf said he would go directly to Afghan President Hamid Karzai about the attacks, according to the Associated Press.
"We have strongly protested and I will, too, God willing, talk about this to Karzai," said Ashraf, speaking in Karachi, reported the AP.
The attacks are the latest in a series of assaults coming from eastern Afghanistan, according to CNN. In 2011, cross-border attacks by militants killed numerous Pakistani soldiers, increasing tensions between the two countries.