Pakistani jets pounded targets in the country’s northwest on Monday as the military waged an offensive against militant safe havens that killed 37 fighters, while insurgents fought back with a roadside bomb that killed six soldiers, the first Army casualties of the operation, the military said.

The offensive marks the end of the government’s policy of trying to negotiate with Pakistani Taliban militants instead of using force to end years of fighting which has killed tens of thousands of civilians and security forces.

Prime Minister Nawaz Sharif, who has promoted the talks, defended the military action during a speech to Parliament on Monday.

Mr. Sharif said the government had tried for more than four months to talk to the militants but their violence continued. He said Pakistan could not become a safe haven for militants.

A spokesman for the militants warned in a statement sent to reporters that international investors, foreign airlines and multinational organisations should leave Pakistan or they’d be considered supporters of the government and fair game.