(AP) — Afghan authorities have arrested the ringleader of a group that staged a brazen attack in Kabul and now believe the assault was coordinated by al-Qaida, an official said Sunday.

Gen. Nahim Baluch, the deputy director of Afghanistan's intelligence service, said that the ringleader — whom he did not name — and several other suspects confessed to their role in the Jan. 18 attack that paralyzed the Afghan capital and left 12 people dead, including seven militants.

"All of them have links with al-Qaida," Baluch said of the suspects.

Afghan officials have previously said that the Haqqani network, a Pakistan-based Taliban faction with close ties to al-Qaida, was behind the assault. Baluch said Sunday that al-Qaida was increasingly directing complex attacks carried out by its close partners.

Analysts and U.S. counterterrorism officials have said al-Qaida leaders have deepened and solidified their relationship with the Taliban and other homegrown militant groups that operate along the porous Afghan-Pakistan border.

Baluch said ammunition and weapons had been seized from the ringleader's house along with paint that he said had been used to disguise an explosives-packed vehicle as an ambulance.

The driver of the fake ambulance blew himself up at a police checkpoint as gunbattles were raging elsewhere in the area.

Baluch spoke at a press conference to explain the government ban on ammonium nitrate, a chemical compound found in fertilizer and often used to make bombs.

He said ammonium nitrate was used in the Jan. 18 attacks as well as an ambush of a guest house in Kabul that killed at least 11 people, including five U.N. staff.

Baluch also claimed that militants in the southern province of Helmand were packing 60 large containers per day with the explosives for use in suicide bombs, blowing up bridges and other attacks.

The Afghan government announced Friday that it was banning the use, production, storage, purchase or sale of ammonium nitrate, which also was used in the devastating 1995 Oklahoma City bombing.

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