Afghanistan–Pakistan relations refer to the bilateral ties between Afghanistan and Pakistan. In August 1947, the partition of British India led to the emergence of Pakistan along Afghanistan's eastern frontier, and the two countries have since had a strained relationship; Afghanistan was the sole country to vote against Pakistan's admission into the United Nations following the latter's independence. Various Afghan government officials and Afghan nationalists have made irredentist claims to large swathes of Pakistan's territory in modern-day Khyber Pakhtunkhwa and Pakistani Balochistan, which complete the traditional homeland of "Pashtunistan" for the Pashtun people. The Taliban has received substantial financial and logistical backing from Pakistan, which remains a significant source of support. Since the Taliban's inception, the Pakistani Inter-Services Intelligence (ISI) agency has been providing them with funding, training, and weaponry. However, Pakistan's support for the Taliban is not without risks, as it involves playing a precarious and delicate game. Afghan territorial claims over Pashtun-majority areas that are in Pakistan were coupled with discontent over the permanency of the Durand Line, for which Afghanistan demanded a renegotiation, with the aim of having it shifted eastward to the Indus River. Territorial disputes and conflicting claims prevented the normalization of bilateral ties between the two countries throughout the mid-20th century. Further Afghanistan–Pakistan tensions have arisen concerning a variety of issues, including the Afghanistan conflict and Afghan refugees in Pakistan, water-sharing rights, and a continuously warming relationship between Afghanistan and India. Nonetheless, the Durand Line witnesses frequent occurrences of suicide bombings, airstrikes, or street battles on an almost daily basis.
Shortly after Pakistani independence, Afghanistan materially supported the failed armed secessionist movement headed by Mirzali Khan against Pakistan. Afghanistan's immediate support of secessionist movements within Pakistan prevented normalised ties from emerging between the two states. In 1952 the government of Afghanistan published a tract in which it laid claim not only to Pashtun territory within Pakistan, but also to the Pakistani province of Balochistan. Diplomatic relations were cut off between 1961 and 1963 after Afghanistan supported more armed separatists in Pakistan, leading to skirmishes between the two states earlier in 1960, and Pakistan's subsequent closure of the port of Karachi to Afghan transit trade. Mohammed Daoud Khan became President of Afghanistan in 1973, Afghanistan—with Soviet support—again pursued a policy of arming Pashtun separatists within Pakistan.
In 2017, the Pakistani military have accused Afghanistan of sheltering various terrorist groups which launch attacks into Pakistan, while Afghan authorities have blamed Pakistan's intelligence agency, the ISI, for funding warlords and the Taliban, and for basing terrorist camps within Pakistani territory to target Afghanistan. There is considerable amount of anti-Pakistan sentiment in Afghanistan, while negative sentiment towards the Afghan refugees is widespread in Pakistan, even in Pashtun-dominated regions. Border tensions between Afghanistan and Pakistan have escalated to an unprecedented degree following recent instances of violence along the widely known 'Durand Line'.
However, former Afghan President Hamid Karzai (in office 2004–2014) has described Pakistan and Afghanistan as "inseparable brothers" along with that he alleged that Pakistan uses terrorism against Afghanistan, which is due to the historical, religious, and ethnolinguistic connections between the Pashtun people and other ethnic groups of both countries, as well as to trade and other ties. Each of the two countries features amongst the other's largest trading partners, and Pakistan serves as a major conduit for transit trade involving landlocked Afghanistan. Both countries are member states of the Organisation of Islamic Cooperation, Economic Cooperation Organization and South Asian Association for Regional Cooperation. The Pakistani government has taken significant action against undocumented migrants inside the country and is expelling all the Afghan people.