"The attack is over and we have cleared the area of all militants, and we will hand over the airport to the Civil Aviation Authority at 12pm (1700 AEST)," a spokesman for the paramilitary Rangers, Sibtain Rizvi, told reporters after nearly 12 hours of fighting.
The attack at Jinnah International Airport in Pakistan's biggest city began just before midnight Sunday and raged until dawn, when the military said that all 10 attackers had been killed after they had stormed two areas equipped with suicide vests, grenades and rocket launchers.
But after authorities initially declared the area cleared, an AFP reporter witnessed fresh gunfire break out inside the airport - where explosions and fires had erupted during the night - prompting security forces to relaunch the operation.
The Tehreek-e-Taliban Pakistan (TTP) group said the attack was in revenge for its late leader Hakimullah Mehsud, who was killed in a US drone strike in November.TTP spokesman Shahidullah Shahid also dismissed the Pakistani government's recent offer of a new round of peace talks as a ruse, and promised more attacks to come.
"Pakistan used peace talks as a tool of war," he told AFP.
"We have yet to take revenge for the deaths of hundreds of innocent tribal women and children in Pakistani air strikes.
"It's just the beginning, we have taken revenge for one (Mehsud), we have to take revenge for hundreds."
Talks to end the TTP's bloody seven-year insurgency in Pakistan have been underway since February, with little clear progress made so far.
The assault will raise fresh concerns about Pakistan's shaky security situation, and questions about how militants were able to penetrate the airport, which serves one of the world's biggest cities.
Officials said the gunmen entered from two sides of the airport at about 11pm local time on Sunday - the terminal used for the hajj pilgrimage to Mecca, and an engineering section close to an old terminal that is no longer in use.
An AFP reporter witnessed three huge blasts as suicide bombers detonated their explosives.
Smoke was seen billowing from the airport as fires raged close to planes parked on the runway, while militants, some dressed in army uniform, clashed with the airport's security force who were backed by police, paramilitary squads and elite commandos.
A senior intelligence official said it appeared the militants had aimed to hijack a plane that passengers were boarding at the main terminal, but that when they were repelled they went on the rampage.
"The passenger plane at Jinnah terminal was their target and when they failed to reach there they destroyed two private terminals in frustration," he told AFP.
After the attack was quelled, a bomb disposal expert in full protective gear was seen walking from the site carrying a suicide vest and a bag full of hand grenades.
Taliban militants have carried out a series of similar raids since rising up against the Pakistani state in 2007 in an insurgency that has claimed thousands of lives.
In 2011, Taliban gunmen attacked the Mehran naval base, which lies close to the Karachi airport, destroying two US-made Orion aircraft and killing 10 personnel in a 17-hour siege.
The group also carried out a raid on Pakistan's military headquarters in the garrison city of Rawalpindi in 2009, leaving 23 dead, including 11 troops and three hostages.
The latest trouble came with tensions already high in Karachi over the arrest in Britain of the exiled leader of Pakistan's MQM party, which dominates politics in the vast city - Pakistan's economic hub and main port through which NATO has long shipped supplies to Afghanistan.
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