A suicide bomber blew himself up on Friday at the headquarters of a banned militant group in Pakistan's Khyber tribal region, killing six persons and injuring 12 others.
The attacker tried to enter the main gate of the headquarters of the Ansar-ul-Islam group in Tirah valley of Khyber Agency, witnesses said.
He detonated his explosives when a watchman stopped him.
Witnesses and local residents said six persons were killed and a dozen others injured.
However, Ansar-ul-Islam leader Mehboob-ul-Haq claimed only one person was killed.
No group claimed responsibility for the attack.
The Ansar-ul-Islam has been engaged in a bitter rivalry with the Lashkar-e-Islam for the past five years.
Dozens of members of both groups have died in clashes between the two groups.