Pakistan’s military resumed air strikes in the troubled North Waziristan region on Monday, a day after the army launched a long-expected military operation against the Pakistani Taliban's main base in the tribal district bordering Afghanistan.

At least 21 militants have been killed in recent air strikes by Pakistani fighter jets in the area, Reuters reported, citing military sources. The military operation was announced just a week after an attack by the Tehreek-e-Taliban Pakistan, or TTP, on Jinnah International Airport in the port city of Karachi, which claimed the lives of 36 people, including 10 militants.

Other details about the latest air strikes could not be confirmed as the army has reportedly imposed a curfew in the region and restricted mobile phone services to isolate the militants, according to Reuters. On Sunday, Pakistan reportedly sent its forces, including troops, artillery and helicopter gunships, to North Waziristan, which is home to some of Pakistan’s most hardened militant groups, including the TTP.

"Our valiant armed forces have been tasked to eliminate these terrorists regardless of hue and colour, along with their sanctuaries," the army reportedly 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."

Pakistani government sources reportedly said early Sunday that at least 150 militants were killed in night-long air strikes on tribal regions in the country's northwest. Although government forces claimed that Uzbek militants were among those killed, according to NBC, local Taliban sources denied the report.

Pakistani combat aircraft targeted at least eight terrorist hideouts in North Waziristan on Sunday, Associated Press reported, citing two intelligence officials. Two officials reportedly claimed that Abu Abdul Rehman al-Maani, who is believed to be the mastermind behind the June 8 attack on the Karachi airport, was among those killed in the air strikes.

Karachi's international airport, which is the nation's busiest, was attacked last Sunday by militants carrying guns and grenades, and launched a protracted firefight with security forces that lasted for hours and stretched into the next morning. A few hours later, the Pakistani Taliban launched a fresh attack on the Airport Security Forces training facility near the airport, forcing all flights to and from Karachi to be temporarily suspended.

The first air strikes by Pakistan's military were conducted less than 36 hours after the attack on the airport, killing at least 15 people in the in the Tirah Valley area of the Khyber tribal district.

On Wednesday, two U.S. drones in Pakistan killed at least 16 militants, about six months after the last drone strike in the area on Dec. 25, which killed four suspected terrorists at a compound near Miramshah, the main town of North Waziristan. U.S. officials had been asked by Pakistani officials at the time to suspend drone strikes in preparation for peace talks with the TTP, which eventually failed.