Who are the Taliban?
The hardline Islamic Taliban movement has proved to be a formidable fighting force in Afghanistan and a major threat to its government.
The Taliban also threatens to destabilise Pakistan, where they control areas in the north-west and have been blamed for a wave of suicide bombings and other attacks.
Many observers now believe that future peace in Afghanistan can only come if the government in Kabul negotiates with the Taliban.
The announcement of Taliban plans to open an office in Qatar in June 2013 is seen as a positive step in those negotiations, but mistrust on both sides remains high.
Hopes for peace talks were equally high early in 2012 before the Taliban in Afghanistan announced in a strongly-worded statement in March of that year that they were suspending preliminary peace negotiations with the US.Austere rule
The Taliban emerged in the early 1990s in northern Pakistan following the withdrawal of Soviet troops from Afghanistan.
A predominantly Pashtun movement, the Taliban came to prominence in Afghanistan in the autumn of 1994.
It is commonly believed that they first appeared in religious seminaries - mostly paid for by money from Saudi Arabia - which preached a hard line form of Sunni Islam.
The Taliban's promise - in Pashtun areas straddling Pakistan and Afghanistan - was to restore peace and security and enforce their own austere version of Sharia, or Islamic law, once in power.
In both countries they introduced or supported Islamic punishments - such as public executions of convicted murderers and adulterers and amputations of those found guilty of theft.
Men were required to grow beards and women had to wear the all-covering burka.
The Taliban banned television, music and cinema and disapproved of girls aged 10 and over from going to school.
Pakistan has repeatedly denied that it is the architect of the Taliban enterprise.
But there is little doubt that many Afghans who initially joined the movement were educated in madrassas (religious schools) in Pakistan.
Pakistan was also one of only three countries, along with Saudi Arabia and the United Arab Emirates (UAE), which recognised the Taliban when they were in power in Afghanistan from the mid-1990s until 2001.
It was also the last country to break diplomatic ties with the Taliban.
Although Pakistan has in recent years adopted a harder line against Taliban militants carrying out attacks on its soil, new Prime Minister Nawaz Sharif - who was elected in May - has said talking to the militants is one of his priorities.
In recent months at least two key leaders of the Pakistani Taliban have been killed in US drone strikes. Mullah Nazir was killed in January and Waliur Rehman was killed in May.
But despite these setbacks for the militants, there is evidence that their influence in Karachi has significantly increased.
What is arguably one of the most internationally criticised of all Pakistani Taliban attacks took place in October 2012, when schoolgirl Malala Yousafzai was attacked on her way home in the town of Mingora.Al-Qaeda 'sanctuary'
The attention of the world was drawn to the Taliban in Afghanistan following the attacks on the World Trade Centre in September 2001.
The Taliban in Afghanistan were accused of providing a sanctuary to Osama Bin Laden and the al-Qaeda movement who were blamed for the attacks.
Soon after 9/11 the Taliban were driven from power in Afghanistan by a US-led coalition, although their leader Mullah Mohammad Omar was not captured.
In recent years the Taliban have re-emerged in Afghanistan and grown far stronger in Pakistan, where observers say there is loose co-ordination between different Taliban factions and militant groups.
The main Pakistani faction is led by Hakimullah Mehsud, whose Tehrik-e Taliban Pakistan (TTP) is blamed for dozens of suicide bombings and other attacks.
Observers warn against over-stating the existence of one unified insurgency against the Pakistani state, however.
The Taliban in Afghanistan are still believed to be led by Mullah Omar, a village clergyman who lost his right eye fighting the occupying forces of the Soviet Union in the 1980s.
Afghans, weary of the mujahideen's excesses and infighting after the Soviets were driven out, generally welcomed the Taliban when they first appeared on the scene.
Their early popularity was largely due to their success in stamping out corruption, curbing lawlessness and making the roads and the areas under their control safe for commerce to flourish.US onslaught
From south-western Afghanistan, the Taliban quickly extended their influence.
They captured the province of Herat, bordering Iran, in September 1995.
Exactly one year later, they captured the Afghan capital, Kabul, after overthrowing the regime of President Burhanuddin Rabbani and his defence minister, Ahmed Shah Masood.
By 1998, they were in control of almost 90% of Afghanistan.
They were accused of various human rights and cultural abuses. One notorious example was in 2001, when the Taliban went ahead with the destruction of the famous Bamiyan Buddha statues in central Afghanistan, despite international outrage.
On October 7, 2001, a US-led military coalition invaded Afghanistan and by the first week of December the Taliban regime had collapsed.
Mullah Omar and his comrades have evaded capture despite one of the largest manhunts in the world.
They are generally thought to be taking refuge in the Pakistani city of Quetta, from where they are guiding the resurgent Taliban.
But the existence of what is dubbed the "Quetta Shura" is denied by Islamabad.
Despite ever higher numbers of foreign troops, the Taliban have steadily extended their influence, rendering vast tracts of Afghanistan insecure, and violence in the country has returned to levels not seen since 2001.
Their retreat earlier this decade enabled them to limit their human and material losses and return with a vengeance.
There have been numerous Taliban attacks on Kabul in the past two years and, in September 2012, the group carried out a high-profile raid on Nato's Camp Bastion base.
In the same month the US military handed control of the controversial Bagram prison - housing more than 3,000 Taliban fighters and terrorism suspects - to the Afghan authorities.
In recent years the Taliban have also increasingly relied on roadside bombs as a means of fighting Nato and Afghan forces.
The exact number of people killed by these devices is difficult to calculate but the interior ministry says they were responsible for killing most of 1,800 Afghan national police personnel who died in 2012.
About 900 Afghan National Army soldiers were killed by roadside bombs during the same time period, estimates suggest.