Two suicide bombers struck outside Pakistan’s main defence complex today, killing more than 70 people in the latest surge of militant violence facing the country's post-Musharraf ruling coalition.

The bombers struck simultaneously at two gates when hundreds of workers were leaving the facility in Wah garrison town, about 20 miles from capital Islamabad.

It was one of the biggest terrorist attacks targeting military installations as Pakistan forces stepped up their campaign against Islamic militants in northern border areas.

Tehrek-e-Taleban Pakistan, an outlawed militant group claimed responsibility for the attack, which was said to be in revenge for military airstrikes in Bajur, a militant stronghold near the Afghan border.

The group threatened similar attacks in other major cities, including Islamabad, unless the military halts its operations.

The complex near the historic city of Taxila is a cluster of about 20 industrial units producing artillery, tank, and anti-aircraft ammunition for the Pakistani Armed Forces. It employs around 25,000 to 30,000 workers.

A senior police official said the bombers blew themselves after failing to get inside the gate.

“All around the gate I saw blood and human flesh," said Rana Tanveer, who was working at a bank about 200 meters from one of the gates where a bomber struck.

"There were bodies lying everywhere and wounded people soaked in blood were screaming for help," said a manager of a petrol station "Many of the wounded were either without legs or hands. I could see body parts hanging on trees," he said.

Police arrested three suspects including a prospective bomber who was trying to flee leaving his suicide jacket inside a mosque. It was the second attack by the Taleban militants this week. More than 35 people were killed in a bombing inside a government hospital on Tuesday, in Dera Ismail Khan town in North West Frontier province.

Rise in militant violence presents the most serious challenge to the fractious ruling coalition struggling to survive after the resignation of President Pervez Musharraf this week. Al Qaeda-linked militants who control large part of northern Pakistan have launched a wave of attacks on the security forces over the past year, bombing military camps, patrols and transport.

The latest surge in the violence came as Pakistani forces launched a major offensive in Bajau tribal region bordering Afghanistan which according to Pakistani and Western intelligence agencies have become the main centre of al-Qaeda and Taleban activities.

Security officials said more than 500 militants and around 30 soldiers have been killed during nearly two weeks of fighting in the region.

Thousands of troops backed by helicopter gunship are involved in the operation. Jet fighters bombed suspected militant hideouts in the area on Wednesday. The fighting has forced more than one hundred thousand people flee the area for safety.

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