Afghanistan\'s President Hamid Karzai has accused Pakistan of firing more than 450 rockets into Afghan territory over the past three weeks. He has blamed Pakistani forces for the attacks, which have killed 36 people, including 12 children. Officials say rocket attacks have hit border areas in the eastern Afghan provinces of Kunar and Nangarhar, where Nato forces have pulled back. There has been no immediate response from the Pakistani authorities. But Afghan border officials say the Pakistani Taliban has moved into the unstable border districts. About 2,000 families have fled since the rocket attacks began, the Associated Press quotes Afghan officials as saying. President Karzai said he raised the issue of rocket attacks with Pakistani President Asif Ali Zardari at a regional anti-terrorism conference in Tehran on Saturday. \"They should be stopped immediately,\" AP quoted President Karzai as saying. And \"if they are not being carried out by Pakistan, Pakistan should make it clear who is behind the attacks,\" he said. But one Afghan official told the BBC that a senior Pakistani official told him that rockets have fallen into Afghan territory as a result of the Pakistani army fighting Taliban forces entrenched in the border areas. President Karzai said he had also discussed the attacks with the Afghan Nato commander Gen David Petraeus and US Ambassador Karl Eikenberry. Meanwhile, an Afghan defence ministry spokesman warned that Afghanistan would retaliate if attacked. \"The government of Pakistan should understand that there will be a reaction for killing Afghan citizens,\" AP quotes Mohammad Zahir Azimi as saying. In recent weeks, Islamabad has also complained of a number of cross-border militant attacks in Pakistan\'s north-west and has lodged official protests with Kabul over the incursions. Securing the long, porous border that divides Pakistan and Afghanistan has been a major challenge for the two countries. The tribal areas on Pakistan\'s western border are infested with various insurgent groups and Afghanistan and Western officials have long complained that Pakistan should do more to curb militants on its soil. Many of the various militant groups along the frontier are closely linked.