The senior Haqqani network leader in Afghanistan, Haji Mali Khan, was captured during a joint NATO-Afghan forces operation, the International Security Assistance Force said Saturday.

Khan was captured Tuesday in Jani Khel district, in Paktiya province, ISAF said.

“This is the arrest of a leading figure of the Haqqani clan,” ISAF spokesman Gen. Carsten Jacobson said. “It is a considerable blow against the Haqqani network.”

The Haqqani insurgent network is widely regarded as one of the most effective militant groups in Afghanistan. Western intelligence officials believe the Haqqanis were involved in the assassination this month of Burhanuddin Rabbani, the chairman of Afghanistan’s High Peace Council, and a June attack on the Intercontinental Hotel in Kabul.

The group has not yet been labeled a terrorist group, but the United States is close to adding it to its terror list. U.S. officials say they are in the final formal review of that process.

The White House praised the capture in a statement Saturday.

“We congratulate the Afghan and ISAF forces for capturing the Haqqani network’s senior commander in Afghanistan, Haji Mali Khan, a key Haqqani leader who facilitated cross-border attacks against our troops,” White House National Security Council spokesman Tommy Vietor said.

Khan is the uncle of Siraj and Badruddin Haqqani — the brothers who lead the network — and worked directly under Siraj, managing bases and overseeing operations in Afghanistan and Pakistan, ISAF said.

Although he was arrested Tuesday, his capture was not announced until Saturday because it took a few days to confirm his identity, NATO spokesman Lt. Col. Jimmie Cummings said.

Khan moved forces from Pakistan to Afghanistan to conduct terrorist activity, ISAF said.

According to ISAF, Khan in the past year established a militant camp in Paktiya province, transferred money to insurgents and help them acquire supplies.

He was heavily armed, but surrendered without incident, ISAF said.

“Haji Mali Khan is a very important member of the Haqqani network. He was an active fighter for the group but also he was helping [Siraj] Haqqani in his administrate work,” said Muhammad Amin, a former member of Afghanistan’s security council and an influential leader in the region. “Whenever Siraj would be busy or away, Mali Khan would attend the meetings for [him]. I think it is quite significant that he has been arrested and for sure Mali Khan has lots of information.”

The Haqqani network was founded by Siraj Haqqani’s father with Pakistani backing to fight against the Soviet occupation of Afghanistan. Still today, the group is believed to maintain ties with Pakistan’s military intelligence, the ISI.

Many of the Haqqani targets have an Indian connection, signs of that association with the ISI.

The links between the ISI and Haqqanis is “very well known,” former joint chiefs chairman Adm. Mike Mullen, who retired Friday, told CNN’s Fareed Zakaria.

“I have argued for the need to sever this link,” he said, adding that the discussion was not a new one for U.S. officials.

The United States has offered a $5 million reward for information leading to the arrest of Siraj Haqqani.

The U.K. Foreign Office praised the capture of Khan.

“As a senior commander within the Haqqani network, his removal from the battlefield will deal a major blow to one of the most dangerous terrorist networks operating in Afghanistan,” said Alistair Burt, foreign office minister for Middle East affairs.

CNN’s Nick Paton Walsh, Tim Lister, Jessica Yellin and journalist Ruhullah Khapalwak contributed to this report.