LAHORE (AFP) - Pakistan has ordered the detention of the leader of a group linked to the 2008 Mumbai attacks which killed 166 people, according to a directive from the interior ministry seen by AFP.

Hafiz Saeed, leader of the charity Jamaat-ud-Dawa (JuD) who has a US$10 million (S$14.2 million) bounty on his head, is to be placed under "preventative detention", according to the order.

JuD, listed as a terror outfit by the United Nations, is considered by the US and India to be a front for Lashkar-e-Taiba (LeT), the militant group blamed for the Mumbai attacks.

But for years the group operated freely across Pakistan, popular for its charity works especially in the wake of natural disasters, and testing Islamabad's resolve to tackle militancy.

The order surfaced hours after Interior Minister Chaudhry Nisar hinted that a crackdown was imminent.

He told reporters in Islamabad earlier on Monday that, given the group had been under observation for years and was blacklisted internationally, Pakistan is "under obligation to take some action".

"The situation will be clear on this by tomorrow," he said, without giving further details.

The order from the interior ministry placed JuD on a watch list and also ordered the detention of four other members in various cities in Punjab.

It was dated Jan 29, but it did not clarify what was meant by "preventative detention" and it was not clear when the action would be carried out.

AFP reporters at a JuD centre in Lahore said no police could be seen there, and JuD sources said police officials had not yet shown them any detention order.

If Saeed is arrested the group will go to court in protest, spokesman Yahya Mujahid told AFP.