Updated

Pakistani authorities, aided by U.S. intelligence, said Thursday they have apprehended more militant chiefs following the capture of the Afghan Taliban's No. 2 figure — arrests that together represent the biggest blow to the militant organization since the U.S.-led invasion in 2001.

The roundups, which could still be under way, occurred as 15,000 U.S., NATO and Afghan forces are pressing the Taliban in their southern Afghan stronghold of Marjah, which had been the biggest town in the area under militant control.

The latest arrests took place late Wednesday and early Thursday when nine militants linked to al-Qaida were nabbed near Pakistan's biggest city of Karachi, where the Taliban's deputy chief Mullah Abdul Ghani Baradar was picked up several days ago.

Others picked up in the recent sweeps included the Taliban's 'shadow' governors in two provinces in northern Afghanistan, according to the official governor of the Afghan province of Kunduz, Mohammad Omar, and two Pakistani intelligence officers.

The Pakistani intelligence officials spoke Thursday on condition of anonymity because they did not have the authority to speak to the media.

Communications intercepted by U.S. authorities played a key role in tracking and arresting the suspects, who were in Karachi buying bomb-making equipment, the officials said. They were taken to Islamabad for questioning.

Many details of the arrests were unclear, including how they were linked to the capture of Mullah Baradar, who effectively ran the Taliban on a day-to-day basis on behalf of the reclusive leader Mullah Mohammad Omar.

But a Pakistani intelligence official said Mullah Baradar has provided "useful" information that has led to the arrests of other suspected militants. The official said Mullah Baradar was traveling in a car on the outskirts of Karachi when he was nabbed along with three of his guards. He said Mullah Baradar was picked up with help from the CIA.

Pakistan security agencies conducted three different raids overnight in Karachi and arrested nine more suspects including three foreigners.

Among those arrested in the three Karachi area raids were:

—Ameer Muawiya, an associate of al-Qaida leader Osama bin Laden who was in charge of foreign al-Qaida militants operating in Pakistan's tribal regions near Afghanistan.

—Akhunzada Popalzai, also known as Mohammad Younis, a one-time Taliban shadow governor in Zabul province and former police chief in Kabul when the repressive regime ruled Afghanistan, according to Mullah Mamamood, a tribal leader in Ghazni province.

—Hamza, who served as a former Afghan army commander in Helmand province, during the Taliban rule.

—Abu Riyan al Zarqawi, also known as Abu Musa, and his local facilitator, Mufti Kifayatullah. According to another Pakistani intelligence official, Zarqawi was involved in dealing with Chechen and Tajik militants operating in Pakistan's northwestern tribal belt on the border with Afghanistan.

The two Taliban shadow governors — Mullah Abdul Salam of Kunduz province and Mullah Mohammad in Baghlan province — were arrested about 10 to 12 days ago in Pakistan, according to Afghan and Pakistani officials.

Both were key figures in the Taliban's expansion to northern Afghanistan, where their forces threatened NATO supply lines coming south from Central Asia and raised alarm that the militants were extending their influence nationwide.

The two Pakistani intelligence officials said Salam was arrested in the Pakistani city of Faisalabad. One of the officials said Salam's arrest was the result of information gleaned from Mullah Baradar.

The Taliban has long operated its own shadow government in the most dangerous parts of Afghanistan, but in recent years, it has bolstered its influence in the north. As of late last year, the Taliban had shadow governments in 33 of Afghanistan's 34 provinces, according to a NATO intelligence official, who spoke on condition of anonymity.

About a month ago, Ebadullah Rahman Niazi, the Taliban's military commander for Laghman province in eastern Afghanistan was arrested in raid by U.S. and Afghan forces, according to provincial Police Chief Gen. Abdul Karim Omaryar. Niazi commanded about 200 militants and oversaw three districts in Laghman, Omaryar said.

It was unclear if his arrest was part of the latest sweep.