The Pakistani Taliban claimed responsibility on Sunday for the first attack in over three years in the northwestern region of Swat Valley on Saturday. The suicide attack left 11 soldiers dead and wounded 13. In a statement sent to media, the extremist group said a lone suicide bomber carried out the attack to avenge the killing and arrests of fellow militants. The bomber detonated his explosives vest near an empty lot where soldiers were playing volleyball. Extremist militants ruled the picturesque Swat Valley from 2007 until a massive military operation routed them in 2009. More than 2,000 Taliban fighters have been driven out of the region, government officials say. Pakistan says militants who escaped from Swat and elsewhere are now operating out of the Kunar province in neighboring Afghanistan. An Afghan official said Pakistani forces shelled Kunar for several hours starting late Saturday, wounding at least four civilians. Faredullah Dehqan, spokesman for the provincial police chief in Kunar, said more than 180 artillery rounds were fired overnight. Afghanistan and Pakistan frequently accuse each other of failing to crack down on extremists that operate along their porous border. On Friday, Afghan President Ashraf Ghani said Pakistan was partly to blame for a wave of recent attacks in Kabul, and that Islamabad was harboring the Afghan Taliban. There was no immediate comment from Pakistan, and it was not clear if the shelling was linked to Saturdays attack. The Pakistani military has been on alert for signs of a Taliban resurgence as it seeks to rebuild civilian institutions and win over the local population as a bulwark against radical ideology. Since being chased out of Swat, the Taliban have carried out revenge attacks against anti-militancy activists and attempted to extort money from business owners in a region where Pakistan has stationed more than 4,000 soldiers. Pakistan’s Prime Minister Shahid Khaqan Abbasi condemned the attack. “No cowardly attack can deter us in pursuing our struggle against the menace of terrorism to its logical conclusion. We will continue our fight till the last trace is rooted out,” the prime minister said in a statement.