WASHINGTON — The Trump administration notified Congress on Wednesday that it was putting $255 million in military assistance to Pakistan into the equivalent of an escrow account that Islamabad can only access if it does more to crack down on internal terror networks launching attacks on neighboring Afghanistan.

The dueling messages sent to Pakistan — promising aid but attaching strings if the country’s counterterror efforts fall short — are part of an increasingly confrontational turn in an alliance that has long been strained.

The United States has provided Pakistan more than $33 billion in aid since 2002. But the annual funding has declined in recent years as Washington became increasingly disenchanted with Pakistan’s quiet support for the Haqqani network and the Taliban, whose attacks have been responsible for the deaths of American troops in Afghanistan.

Still, American officials have long recognized that Pakistan has tried to crack down on terror groups, and plays an important role in facilitating supply shipments to the United States military in Afghanistan.