Jim Mattis has urged Pakistan to redouble efforts to halt insurgents staging attacks across the border in Afghanistan.
Mattis arrived in Pakistan on Monday for his first visit since assuming his post, meeting with Prime Minister Shahid Khaqan Abbasi and other officials.
Mattis reportedly stressed how Pakistan plays a key role in maintaining the stability of Afghanistan.
A Pentagon statement said Mattis reiterated that Pakistan must intensify its efforts to confront militants and terrorists operating within the country.
He was apparently referring to the Taliban and its allied Haqqani network based in northwestern Pakistan.
Under a new Afghan strategy adopted this year, US President Donald Trump is deploying more troops and expanding airstrikes against the Taliban in Afghanistan.