Four Taleban suicide bombers, dressed as police and women, attacked the main United Nations compound in Herat city, a commercial hub in Afghanistan’s west, on Oct. 23. All four were killed and there were no casualties among UN staff.

While the attack was repelled successfully, it caused concern for Afghan and NATO-led forces because Herat, once largely stable, is seen as an early candidate for the transfer of security responsibility from foreign forces to Afghans.

The pace and scope of such security transfers will determine when and how many foreign troops can leave Afghanistan. US President Barack Obama, who will review his Afghanistan war strategy next month, has promised to begin drawing down US forces from July 2011, if conditions on the ground allow.

Sayed Ansari, a spokesman for Afghanistan’s National Directorate of Security (NDS), said one of the three detained men, identified as Noor Mohammad, had been responsible for transporting the four suicide bombers from Quetta in Pakistan.

The bombers were taken from Quetta through southern Kandahar province, the birthplace of the Taleban, to Herat, Ansari said.

Ansari said the attack was directly connected to the “Quetta Shoura,” the senior Afghan Taleban leadership based in Quetta in Pakistan’s Baluchistan across the border from Kandahar.

“The attack took place under orders from Mullah Esmatullah Samangani, who is a current member of the Taleban’s Quetta Shoura and now lives in Pakistan,” Ansari said.

Most of the senior members of the Afghan Taleban, including their leader Mullah Omar, fled to neighboring Pakistan when US-backed Afghan forces toppled the hard-line government in late 2001.

Afghan and Western officials believe Mullah Omar is still somewhere in Quetta and directing attacks against the government of President Hamid Karzai and his Western backers.

Ansari said two Pakistani nationals, who he identified only as Hekmat and Muneer, were also involved in preparing the four suicide bombers in Quetta.

He said the other two men who had been detained were car dealers in Herat city who had supplied a vehicle that was used in the suicide attack.

He said the three were detained in Herat last week and that a fourth man, who resisted arrest, had been killed.

One of Afghanistan’s largest cities, Herat is under the regional command of Italian troops and had enjoyed relative calm compared with Taleban strongholds in the south and east.