"I think Baghdadi is alive", Mr. Mattis told reporters at the Pentagon.
The funds being withheld is part of a Pentagon program called Coalition Support Fund, which aims to reimburse U.S. allies and partners for their counterterrorism operations, Xinhua news agency reported.
Those clawbacks come from the almost $900 million the usa was supposed to reimburse Pakistan for its counterterrorism efforts in 2016.
The Pentagon is withholding hundreds of millions of dollars meant to reimburse Pakistan for its fight against terrorist groups, citing Islamabad's failure to take "sufficient action" against the Haqqani Network, an offshoot of the Taliban based in Pakistan.
Secretary of Defense James Mattis has informed Congress that the USA is withholding $50 million in funding from Pakistan because he was unable to certify that Islamabad "has taken sufficient action against the Haqqani Network", a branch of the Afghan Taliban.
Directly dealing with Pakistan's support for terrorists fighting the US and its allies in Afghanistan would mark a significant departure from what America has done in the past.
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Pakistan was allotted Dollars 900 million aid through the special fund by the United States.
"This decision does not prejudge the conclusions of the White House review of South Asia strategy, which is still ongoing", he said.
The Pentagon highlighted that Pakistan could still receive reimbursement funding for operations in 2017, some $400 million, should the Pakistani military launch offensives against the Haqqani Network.
Military Financing Programme' for Pakistan may be made available unless the secretary of state certifies to the committees that Islamabad is taking action against terrorist groups.
The move comes amid the Trump administration's review of USA policies in Afghanistan.
Relations between the two allies have been frayed over the past decade, with the USA officials constantly accusing Pakistan of what they term its unwillingness to act against terror groups.
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Of the rest, $300 million had already been reprogrammed for other purposes, but had not been previously reported.
As he and Vice President Mike Pence arrived at the Pentagon for an update on the fight against ISIS, Trump was asked whether more troops would be sent to Afghanistan.
This is for the second consecutive year that the US Defence Secretary has refused to certify to Congress, as mandated under National Defence Authorisation Act (NDAA), that Pakistan has taken satisfactory action against the Haqqani network.
Mattis' failure to certify that Pakistan has aggressively cracked down on terror groups may be part of the Trump administration's overall effort to put pressure on Pakistan, as militant groups in the region often operate with far too much latitude in Afghanistan.
Pentagon spokesman Stump said the decision did not "reduce the significance of the sacrifices that the Pakistani military has undertaken over previous years".
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