Donald Trump has accused Pakistan of "lies and deceit" in his first tweet of the year.
The US president said Islamabad had played American leaders for "fools", a reference to frustrations that Pakistan is not doing enough to control terrorism.
Mr Trump wrote: "The United States has foolishly given Pakistan more than 33 billion dollars in aid over the last 15 years, and they have given us nothing but lies & deceit, thinking of our leaders as fools. They give safe haven to the terrorists we hunt in Afghanistan, with little help. No more!"
Pakistani foreign minister Khawaja Asif tweeted that his government was preparing a response that "will let the world know the truth".
Mr Trump returned to Washington on Monday afternoon after a break at his private Mar-a-Lago resort in Florida, a stay which culminated in a New Year's gala.
Before his departure, the president tweeted that "there was much work to be done" on his return.
The president is hoping for more legislative achievements after his pre-Christmas success on taxes.
He plans to host Senate majority leader Mitch McConnell of Kentucky and House Speaker Paul Ryan of Wisconsin at Camp David next weekend to map out the 2018 legislative agenda.