The Taliban claimed responsibility.
After the September 11 terror attacks, IMU militants fought with the Taliban in Afghanistan but were wiped out by US forces by 2002.
Founded in the 1980s, HUM sent members to fight in Afghanistan alongside the Taliban and against Indian security forces in the disputed Himalayan territory of Kashmir in the 1990s.
Or, as migrants themselves put it: "I had problems with the Taliban and had to leave Afghanistan in a hurry".
Malala Yousafzai, the teenage Pakistani education campaigner shot on a school bus in 2012 by a Taliban gunman, and Kailash Satyarthi, an Indian children's rights activist.
Following the massacre by the Pakistani Taliban of 141 people at a school in Peshawar this week, Pakistan's prime minister, Nawaz Sharif, vowed his country would "continue the war against terrorism until the last terrorist is eliminated".
"It has become a norm for this media to brand the defenders of the honour of Prophet Muhammad as terrorists," the Taliban statement complained.
Also on Friday, a leading Pakistani Taliban splinter group praised the "blessed attacks in France" but had harsh words for governments and media in the Islamic world, who the group said had not condemned the magazine forcefully enough.
He also suggested that a key element of the UK contribution would be passing on the experience gained during previous operations in Iraq – the last British troops to withdraw from the country left as recently as May 2011 – and also lessons learned during the UK military's 13-year war with the Taliban in Afghanistan where troops dealt routinely with roadside bombs and other explosive devices.
Millions of Afghans have returned to their homeland since the international community uprooted the Taliban regime in 2001, but more than 2.5 million are thought to remain – the second largest refugee population in the world.
They disrupt Taliban supply lines, search for caches of explosives, clear the roads of land mines.
