* Ethnic Uzbek commander among 80 militants killed -army
* Air assault follows militants' attack on Karachi airport
* US drones also struck Taliban targets in region last week (Adds defence ministry comment, details)
By Haji Mujtaba
MIRANSHAH, Pakistan, June 15 (Reuters) - Pakistan sent troops, artillery and helicopter gunships to the troubled North Waziristan region on Sunday in a long-expected military operation just a week after a deadly insurgent attack on the country's biggest airport.
The Taliban and ethnic Uzbek fighters holed up in North Waziristan - home to some of Pakistan's most feared militants and al Qaeda commanders - have both claimed responsibility for last Sunday's commando-style attack on Karachi airport.
The brazen all-night assault all but destroyed prospects of peace talks with the militants, who are fighting to topple the Pakistani government and impose a strict Sharia-based theocracy in the nuclear-armed nation.
"Our valiant armed forces have been tasked to eliminate these terrorists regardless of hue and colour, along with their sanctuaries," the army said in a statement.
"With the support of the entire nation, and in coordination with other state institutions and law enforcement agencies, these enemies of the state will be denied space anywhere across the country."
It was not known where in North Waziristan, a mountainous ethnic Pashtun region on the Afghan border, the operation was taking place.
Prime Minister Nawaz Sharif had long opposed outright military action, stressing the need to bring the Taliban to the negotiating table, and the decision to send troops means that the powerful army had once again won the upper hand in Pakistan.
It also raises the risk of revenge attacks by Taliban insurgents outside the tribal region after the Taliban vowed to strike back and hit Pakistani security and government targets.
The army has resorted to periodic air strikes against militant positions but has not been involved on the ground. Earlier on Sunday fighter jets pounded militant hideouts in the region, killing at least 80 insurgents.
"We as a government tried our level best to resolve this crisis through dialogue," the defence ministry said in a statement. "We were frustrated through attacks on innocent Pakistanis and damage to national assets."
It added: "This operation will continue until the surrender or elimination of the enemy.
In anticipation of more violence, families have been fleeing North Waziristan into other parts of Pakistan as a climate of fear has gripped the lawless mountainous region.
It was not immediately known whether there were any civilian casualties. Journalists' movements are restricted in the ethnic Pashtun region where the army has imposed a curfew, and verifying official or insurgent accounts is next to impossible.
Military sources told Reuters that Pakistan had sent 40,000 troops to the region for the operation, bringing the total to 80,000 and sealing off the border with Afghanistan.
"Around 40,000 additional troops have been moved into North Waziristan for the operation, backed by artillery and helicopter gunships," said a military official.
"The border with Afghanistan has been sealed off with thousands of troops to keep militants from escaping to Afghanistan."
Pakistani authorities fear that militants might try to seep through the porous border and flee the area along with civilians, possibly into neighbouring Afghanistan, making it harder to kill or capture them.
CLIMATE OF FEAR
The army said ethnic Uzbeks accounted for most of those killed in the earlier air assault.
"Fighter jets targeted militant hideouts in the village of Dagan near the Pakistani-Afghan border," said one source in the regional capital of Miranshah.
"An important Uzbek commander, Abdul Rehman, has been killed in the air strike," he said, adding that Rehman was directly involved in masterminding the Karachi airport attack.
Military sources said a number of ethnic Uighur militants, who operate alongside Uzbeks and share a similar Turkic language with them, had also been killed.
The official account could not be independently verified and there was no immediate comment from the Taliban.
China believes that Uighur separatists based in Pakistan's tribal areas are behind an insurgency against Han Chinese in its restive Xinjiang province, although their exact numbers in Pakistan are unknown.
After the Karachi attack, in which 38 people were killed, U.S. drones conducted the first air strikes in Pakistan since the start of the year, hitting militant positions.
Pakistani air force jets have also been pounding militant hideouts and there has been increased speculation that the army is preparing for a major ground and air offensive in the region.
Officials said a curfew had been imposed in the region and the army was setting up more checkpoints to improve security. (Writing by Maria Golovnina; Additional reporting by Asim Tanveer, Jibran Ahmed and Mehreen Zahra-Malik; Editing by Stephen Powell)