(Adds details, background)
By Haji Mujtaba
MIRANSHAH, Pakistan, June 16 (Reuters) - Pakistani fighter jets resumed air strikes in North Waziristan on Monday, a day after the army announced the start of a major military operation to flush insurgents out of the volatile region bordering Afghanistan.
Military sources said combat aircraft pounded targets in the region's Shawal sector, killing at least 21 militants.
Independent confirmation or other details were not immediately available in a region where journalists are not allowed to operate freely, and where the army has imposed curfew and turns off mobile phone services to undermine the insurgency.
On Sunday, Pakistan sent troops, artillery and helicopter gunships to North Waziristan in a long-expected military operation seen as a response to a deadly insurgent attack on its biggest airport a week ago.
The all-night attack on Karachi airport by a band of highly trained Uzbek fighters all but destroyed prospects for 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.
Prime Minister Nawaz Sharif, who preferred peace talks, has been under pressure from hawks in the army as well as the United States to launch a major operation against militants in North Waziristan, part of the largely lawless areas bordering Afghanistan.
After the Karachi attack, public opinion also appears to have swung in favour of a military operation, even if military action in North Waziristan means a higher risk of revenge attacks by the Taliban outside the tribal region.
"Operation at last!" The Nation daily said in a front-page headline. Security is visibly tighter in the capital, Islamabad, as well, with street patrols by paramilitary Rangers and police.
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 the June 8 commando-style attack on Karachi airport. (Additional reporting by Asim Tanveer; Writing by Maria Golovnina; Editing by Clarence Fernandez)