UPDATE 3-Pakistan spy chief briefs parliament on security

(Updates with latest military offensive in Bajaur)

By Simon Cameron-Moore

ISLAMABAD, Oct 8 (Reuters) - Pakistan's new military spy chief briefed lawmakers on the internal security threat, and conflict in tribal lands seen as al Qaeda and Taliban havens, in a rare closed door session of parliament on Wednesday.

"It will help evolve a national consensus and formulate a national policy on how to tackle growing terrorism and extremism," Defence Minister Ahmed Mukhtar told Reuters.

"Everybody knows the security situation in the country," he said, as troops sealed off roads leading to parliament and government buildings, and helicopters hovered over Islamabad.

The briefing by Lieutenant-General Ahmad Shujaa Pasha came as troops backed by helicopter gunships killed 20 militants in Bajaur in the northwest

Pakistan is reeling from a fresh wave of bomb attacks after a lull that followed an election in February that brought a civilian government to power and signalled the end of the road for former army chief Pervez Musharraf's presidency.

A suicide truck bomb that killed 55 people and destroyed the Marriott Hotel in Islamabad on Sept. 20 delivered a fresh shock to a country whose best known politician, Benazir Bhutto, was assassinated in a suicide bomb and gun attack last December.

The six-month old coalition, headed by Bhutto's party, is under pressure from its U.S. ally to use more force against the militants fuelling the insurgency in Afghanistan, and harbouring Al Qaeda planners plotting attacks in the West.