Head of the Pakistani paramilitary forces, Rizwan Akhtar, had earlier stated the attackers share resemblance with Uzbeks, Xinhua reported Wednesday.
Uzbek militants, who are affiliated with the Pakistani Taliban and al-Qaeda, had been hiding in North and South Waziristan for years.
Waziristan is a mountainous area in Federally Administered Tribal Areas (FATA) region in north-western Pakistan bordering Afghanistan.
"Usman Ghazi, the leader of the Islamic Movement of Uzbekistan (IMU), claimed responsibility for Sunday's terrorist attack on Karachi's Jinnah International Airport in a statement published on a Pakistani jihadist forum Tuesday," Xinhua quoted pakistanrisk.com, a previously unknown website, as saying.
The website said it offered strategic analysis of political and security issues in Pakistan.
Pakistani Taliban had earlier claimed responsibility for the attack that has claimed lives of nearly 30 people.
The Tehreek-e-Taliban Pakistan (TTP) spokesman Shahidullah Shahid has now claimed that it was a joint Taliban and IMU operation.
The Uzbek militant group described the attacks as revenge for Pakistani air-strikes in North Waziristan May 21 that targeted areas populated by Uzbek and other foreign militants.
"The IMU claims to have destroyed fighter jets and US drones that were not visible to commercial airline passengers at the airport. There is no evidence to corroborate this claim. It is highly unlikely that drone aircraft would operate from an airport in Karachi, a congested megacity," the website said.
Members of the Uzbek militant outfit are believed to be hiding in Waziristan
Uzbek fighters had been expelled from South Waziristan by a Taliban leader Mulla Nazir after the locals had turned against them for their harsh behaviour with the tribesmen. They had then moved to North Waziristan and mostly live in Mir Ali area. The area had been focus of the military air-strikes in recent weeks.
Ghazi, the IMU leader, called on Muslims in Pakistan to wage a war against the Pakistani state, according to the Pakistanrisk website.
Pakistani security personnel have asserted that there were ten attackers.
The IMU statement purports that ten of its terrorists died in the attempted siege.