Mattis's optimism is at odds with analysts including the USA inspector general for Afghanistan reconstruction, who said in a report in August that a group affiliated with Islamic State has laid down roots in the country, part of a broad deterioration that has seen a record number of Afghan civilians killed.
The Chairman of US Joint Chiefs of Staff has accused Pakistan's main intelligence agency, Inter-Services Intelligence (ISI) directorate, of having ties with terrorists.
President Donald Trump announced in August a plan to end America's longest war and eliminate a rising extremist threat in Afghanistan.
More than 3,000 US troops are being added to about 11,000 already in Afghanistan, according to Mattis.
"In the six weeks since the president made his announcement, this committee and the Congress, more broadly, still does not know numerous crucial details of this strategy", McCain said. An additional 6,800 North Atlantic Treaty Organisation and coalition troops are there to assist about 320,000 Afghan national security forces.
European ambassadors speaking in Washington last week said they would do everything possible to protect companies based in Europe and that continue to do business with Iran, from reimposed USA sanctions.
"Getting the Afghan forces to the point where they can provide security for their country with a minimum amount of global support".
Some of the additional US military advisers will be assigned to work with an Afghan corps, a large unit that includes thousands of soldiers. As a presidential candidate, he vowed to "rip up" the deal, which was signed under his predecessor, Barack Obama.
"The president has to consider more broadly things that rightly fall under his portfolio of looking out for the American people in areas that go beyond the specific letters of the JCPOA - in that regard I support the rigorous review that he has got going on right now", he said.
Mattis introduced a new acronym to explain the Trump administration's plan: R4+S.
Mattis says more than 3,000 additional USA troops are being sent to Afghanistan to reinforce the roughly 8,400 American forces now stationed there. Trump's tough words about Pakistan, a troubled US security partner, infuriated Islamabad, which has denied the country provides safe havens for the Taliban.
The United States in 2012 designated the Pakistan-based Haqqani network as a terrorist organisation.
"That's a tactical effect that will make the Afghan army bolder, and it will give them more opportunities militarily to take the fight to the enemy", Mattis said. Mattis said the new deployments will enable the NATO-led mission to reinforce training and advisory support at the battalion and brigade levels and to provide them with enhanced coalition air support.
Dunford says about $5 billion of the total expense is required to support the Afghan security forces. "As a result, the Taliban expanded territorial and population control and inflicted significant casualties on the Afghan army and police, while the campaign lost momentum".