The relations between the two countries have been strained lately after President Donald Trump hit out at Pakistan for providing safe havens to terror groups that kill Americans in Afghanistan.
"We intend to work with Pakistan in order to take the terrorists down. I think that's what a responsible nation does," Mr Mattis said at a media briefing yesterday.
The Trump administration recently notified the US Congress that it has given $255 million worth of conditional military assistance to Islamabad that it can only be accessed if it takes more action against terror groups.
"The (state) department is placing a pause on spending those funds and on allocating them to any specific FMF sales contracts," a state department official told news agency PTI.
The US took this decision as it had two options -- either to give this money to Pakistan or return it back unused to the treasury department.
Secretary of State Rex Tillerson said on August 22 that, "Pakistan must adopt a different approach, and we are ready to work with them to help them protect themselves against terrorist organisations. We are going to be conditioning our support for Pakistan and our relationship with them on them delivering results in this area."
According to The Wall Street Journal, the move to hold back on the funds is the first in a series of possible actions Mr Tillerson and others previewed last week.
"Other steps to turn up the heat on Pakistan could include sanctioning Pakistani government officials and stepping up US drone strikes, as well as further reductions the in US aid," the financial daily said.
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