Peshawar, Pakistan ? Pakistan sent helicopter gunships and troops to attack Taliban militants in a district covered by a peace deal after strong U.S. pressure on the nuclear-armed nation to confront insurgents advancing in its northwest.

At least 31 people were killed on Sunday in the operation, which sent some residents of Lower Dir district fleeing carrying small children and few belongings.

The push appeared to endanger a peace pact struck with Taliban militants in neighboring Swat Valley, although a top official insisted the deal was “intact.” Another official demanded the insurgents disarm, but a Taliban spokesman said the militants would not give up their weapons.

The Lower Dir offensive also came ahead of Pakistani President Asif Ali Zardari’s scheduled meeting with President Barack Obama in early May, but Pakistani officials denied outside pressure influenced the move.

British Prime Minister Gordon Brown is expected in Islamabad today for talks with Pakistani leaders.