(Adds Taliban comment, another attack)
By Syed Raza Hassan
ISLAMABAD, June 9 (Reuters) - Taliban militants disguised as security forces stormed Pakistan's busiest airport on Sunday and at least 27 people were killed in a dramatic night-long battle at one of the country's most high-profile targets.
The assault on Jinnah International Airport in Karachi, Pakistan's sprawling commercial hub of 18 million people, all but destroys prospects for peace talks between the Pakistani Taliban and the government of Prime Minister Nawaz Sharif.
It also deals a heavy blow to Sharif's efforts to attract foreign investors to revive economic growth and raises questions about security at the country's main installations.
In a possible change of tack, the Taliban said their mission was to hijack a plane - a break from their usual pattern of roadside bombs and suicide bomb attacks.
"The main goal of this attack was to damage the government, including by hijacking planes and destroying state installations," said Shahidullah Shahid, a Taliban spokesman.
The violence began just before midnight when 10 gunmen wearing military uniforms and armed with automatic rifles and rocket-propelled grenades shot their way into the terminal building after arriving at the cargo terminal in two mini-vans.
The militants then split into two groups, with one attacking a gate called Fokker to create a diversion and the other storming the cargo terminal, police said.
"They operated in pairs. That's why their bodies were found lying in pairs," said senior police officer Raja Umar Khattab, adding the militants had fired rockets at passenger planes but missed. "It seems there was some ill-planning on their part."
Officials said no aircraft had been damaged.
Another security source said the militants were highly trained and carried large backpacks filled with dried fruit and water, suggesting they were in for a long siege.
Gun battles raged through the night until security forces regained control of the airport at dawn. Passengers were evacuated and all flights were diverted. The government said security was being stepped up at all airports.
"We need to keep extremely vigilant," Shujaat Azeem, special assistant to Sharif on aviation, said in a statement.
The Pakistani Taliban, an alliance of insurgent groups fighting to topple the government and set up a sharia state, said they carried out the attack in response to air strikes on their strongholds near the Afghan border.
MILITANTS "APPEAR TO BE UZBEK"
Pakistan's paramilitary force said that the attackers were ethnic Uzbeks. Pakistani officials often blame foreign militants holed up in lawless areas on the Afghan border for staging attacks alongside the Pakistani Taliban around the country.
"Three militants blew themselves up and seven were killed by security forces," Rizwan Akhtar, the regional head of the paramilitary Rangers, said in televised remarks. "The militants appear to be Uzbek."
The death toll included airport security guards and workers with Pakistan International Airlines.
In separate, unrelated violence, 24 Shi'ite Muslim pilgrims were killed in a suicide attack near Pakistan's border with Iran, an official said. A radical Sunni Moslem group claimed responsibility.
As violence spiralled, a suspected Taliban suicide bomber rammed a truck into a military checkpoint on the border with Afghanistan, killing four soldiers, military officials said.
Sharif came to power last year promising to find a negotiated solution to years of violence but after the attack on the airport, the peace process looks in trouble.
Karachi is Pakistan's biggest city and commercial hub, home to a vibrant stock exchange, the central bank and the country's main port. But it is also a violent and chaotic place where Taliban militants and criminal gangs operate freely underground.
At the airport, gun battles went on for five hours and television pictures showed fire raging as ambulances ferried casualties away.
At least three loud explosions were heard as militants wearing suicide belts blew themselves up.
By dawn on Monday, the army said the airport had been secured but heavy smoke rose above the building.
"Ten militants aged between 20 and 25 have been killed by security forces," said a spokesman for the Rangers. "A large cache of arms and ammunition has been recovered from the militants."
Peace talks between the government and the Pakistani Taliban had been failing in recent months, already dampening hopes of reaching a negotiated settlement with the insurgents, who continue attacks against government and security targets. (Writing by Maria Golovnina; Additional reporting by Gul Yousufzai in QUETTA, Haji Mujtaba in MIRANSHAH and Mehreen Zahra-Malik in ISLAMABAD; Editing by Robert Birsel and Nick Macfie)