ISLAMABAD In a commando-style attack carried out with military precision, militants wearing Pakistani uniforms burst into the country's busiest airport under cover of darkness in one of the most audacious attacks in Pakistan in years.
Pakistani military officials said the attackers were ethnic Uzbeks who operate under the wings of the Pakistani Taliban in bases dotted around the lawless areas straddling Pakistan's border with Afghanistan.
Uzbek jihadists are a particularly feared force. They are believed to number no more than a few hundred, but the fact that they have no tribal attachments in Pakistan means they are particularly ruthless and indiscriminate.
A smaller force of Chinese Uighur fighters also operates in the region, usually in conjunction with the Uzbeks with whom they share a similar Turkic language and culture, officials say.
"Uzbeks and Chinese Uighurs are holed up in the mountains between South and North Waziristan," said Imtiaz Gul, a security expert in the Pakistani capital, Islamabad.
"Because they enjoy the (Taliban's) social and political shelter they have become instrumental in what (the Taliban) are carrying out. Many of them have become foot soldiers for the missions of the (the Taliban)."
Ethnic Uzbek fighters in Pakistan are the remnants of a once-powerful Islamic Movement of Uzbekistan (IMU), a Jihadist group set up in the early 1990s with the aim of toppling Uzbek President Islam Karimov and setting up a Sharia state in the former Soviet Central Asian state.
Squeezed out of Uzbekistan by Karimov's increasingly hardline tactics, IMU militants trickled out of the country throughout the 1990s and eventually joined forces with the Taliban fighting U.S.-led forces in neighboring Afghanistan.
The IMU was all but destroyed in the first years of fighting that followed the 2001 invasion of Afghanistan, experts say, but its fighters later regrouped and settled alongside Taliban commanders in Pakistan. Now it is once again a formidable force.
Pakistan's paramilitary Rangers said after Sunday's attack that it was carried out by Uzbek fighters, even though it was the Taliban's central command that initially claimed responsibility.
Abdullah Bahar Mehsud, a senior Pakistani Taliban commander, told Reuters it was a joint Taliban-Uzbek effort.
"It was a joint operation in which our Uzbek brothers played an important role," he said. "I can't tell you about the nature of support they provided us with, but in operations such as Karachi airport, one group provides fighters, another arranges finances for weapons and explosives."
Pakistan Risk, a website monitoring political and security issues in the country, quoted the IMU as saying that its fighters were behind the Sunday raid in Karachi.
It is not unusual for different Jihadist groups to claim responsibility for the same assaults, and the dual claim only underscored the close relationship between the two.
Pakistan Risk wrote in its report that the attack was revenge for Pakistani air strikes in the tribal belt.
"The Uzbek militant group ... describes the attacks as revenge for Pakistani air strikes in North Waziristan on May 21 that targeted areas populated by Uzbek and other foreign militants," it said.
Pakistan Risk also posted pictures of 10 smiling men wearing black turbans whom it described as the Sunday attackers.
"Statements from the IMU in recent weeks have indicated a growing disdain not just for the Pakistani military, but also for the local population in North Waziristan," it said.
"For example, an IMU militant complained in a recent missive that tribesmen in North Waziristan are placing Pakistani flags above their homes."
(Writing by Maria Golovnina; Additional reporting by Jibran Ahmed; Editing by Nick Macfie)