Tribesmen in the South Waziristan region of Pakistan say they will raise a force of 1,800 armed men to capture suspected al-Qaeda militants.
The tribesmen have been accused of harbouring al-Qaeda members
The force would be the biggest armed militia - or Lashkar - so far raised for such a purpose.
The decision to form it was made by the Ahmedzai Wazir tribe in the main town of Wana, 400 km southwest of Peshawar.
It is the first time that all the clans and sub-clans of the region have unified against al-Qaeda.
Return to arms
The main objective of the newly formed force is to make foreigners in South Waziristan register their names under the terms of an agreement made last month between tribal elders and the authorities.
The force is due to gather on Tuesday at Wana, when more details of their deployment and terms of reference are expected to emerge.
But already its formation has been criticised.
A prominent local tribal militant, Neik Mohammad, told the BBC on Monday that no foreigner was hiding in the South Waziristan area.
He has warned that he and his colleagues will again take up arms if the government violated a pledge made in last month's agreement not to launch another offensive in South Waziristan.
Mr Mohammad argues that there is no provision for registration of foreigners in the agreement.
"It does not contain any clause for registration," Mr Mohammad said.
But that allegation has been denied by the governor of North West Frontier Province, who on Monday said that the agreement clearly stipulates that all foreigners were obliged to register with the authorities.
A statement released by the governor added that the deadlines for them to register have been extended several times after requests were submitted on their behalf through negotiators.
The statement warned of using "other options" if foreigners do not get registered.
Foreign ministry spokesman Masood Khan said there would be no compromise if the demand is not met.
"When they register it would become evident whether or not they are terrorists," he said.
" If they are not terrorists, they have nothing to hide, they should come forward and register with the authorities. There cannot be any question or compromise on that."
The decision to raise the force comes hours before another deadline set by the government for foreigners to register is due to expire.