PESHAWAR, Pakistan — Pakistan declared “open war” Friday on Afghanistan, after the two South Asian neighbors traded overnight attacks in a sharp escalation of their long-running dispute. Both sides claimed to inflict heavy damage in the renewed fighting, which threatens to further destabilize a region where terrorist groups such as the Islamic State and Al Qaeda are trying to remobilize. Tensions between the two countries, which share a 1,600-mile border, have been simmering for months as they struggle to maintain a Qatar-mediated ceasefire they reached in October, with occasional cross-border skirmishes. Pakistan, which is struggling with a surge in militant attacks since the United States withdrew from Afghanistan in 2021, says the attackers are using Afghanistan as a base. The Taliban, which seized power as the U.S. withdrew, denies harboring militants. The latest violence began Thursday night when the Taliban launched what it called retaliatory attacks on military installations in northwest Pakistan.…