Mattis also warned Pakistan of global "diplomatic isolation" and losing its Non-NATO ally status if it failed to take action against safe havens to terrorists on its soil.
"If our best efforts fail, President Trump is prepared to take whatever steps necessary," Mattis told members of the powerful House Armed Services Committee during a Congressional testimony on South Asia and Afghanistan yesterday.
He was asked a series of questions by Congressmen who expressed their frustration on Pakistan not taking actions against terror groups.
"Right now, I would like to think we will be successful," Mattis said. "With the growing consensus against terrorism, they'll find themselves diplomatically isolated."
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"There is an awful lot of advantage to Pakistan of coming online with the international community, and we have to stay focused there, but the penalties are just as significant as the advantages if they choose to go a different direction," he said.
"But for right now, the US needs to try one more time to make this strategy work with them by, with, and through the Pakistanis," he said.
Mattis' tough talk on Pakistan, came as Pakistan Foreign Minister Khwaja Asif is visiting the US as part of efforts to rebuild bilateral ties frayed after President Trump accused Islamabad of sheltering terror groups.
President Trump announced his Afghanistan and South Asia policy in August in which he adopted a tough policy against Pakistan.
In a meeting with the Secretary of State Rex Tillerson, Asif defended his country's role in the war against terrorism.
However, Mattis told lawmakers that while the US is adopting "a whole of government approach" on Pakistan, it is also aligning NATO countries on this.
"What you're going to see is 39 nations all in the NATO campaign working together to lay out what it is we need Pakistan to do, he said.
"What we are doing right now is we are aligning what Department of Treasury, Department of Defence, the Intelligence Committee, Department of State, say, this is what we must ask Pakistan to do to change its behaviour, he added.
"Pakistan has lost more troops in this fight against terrorist than nearly any country out there. And yet at the same time, as you know, there's been some parsing out where some terrorists have been allowed safe havens. We're out to change that behaviour and do it very firmly, Mattis asserted.
As part of this, Mattis said there would be exchange of high-level visits between the two countries.
Mattis said he and the Secretary of State Rex Tillerson will soon visit Islamabad.
"I will go in and we have (NATO) Secretary General Stoltenberg's very clear support for this in his advocacy as the Secretary General of NATO. So we're going to continue to build this up in an international way with a whole of US government argument for the Pakistanis to work in their own best interest and ours," Mattis said.
After holding talks with Asif, Tillerson yesterday said that the US is concerned over the future of the government in Pakistan and wants to ensure long-term stability in the country.
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