New Delhi, Feb. 28 -- Pakistan and Afghanistan exchanged cross-border attacks overnight in a dramatic escalation of tensions that led Pakistan's defense minister to say on Friday that the two countries are in a state of "open war."

Afghanistan launched an attack on Pakistan late Thursday, saying it was in retaliation for deadly Pakistani airstrikes on Afghan border areas Sunday. Pakistan then carried out airstrikes in Kabul and two other Afghan provinces early Friday, saying it targeted military installations.

Tensions have been high for months. Border clashes in October killed dozens of soldiers, civilians and suspected militants. Pakistan accuses Afghanistan's Taliban government of harboring militant groups that stage attacks against ...