The US President Donald Trump is set to unveil a new US strategy in Afghanistan after meeting with his national security team at Camp David on Friday.

Trump will address the nation on Monday night from Fort Myer in Arlington, Virginia, "to provide an update on the path forward for America's engagement in Afghanistan and South Asia," according to a statement from the White House.

Trump and his team have been in talks for months about a strategy to pursue in Afghanistan.

On Sunday, the US Defense Secretary James Mattis said that Trump has made a decision on the United States' strategy for Afghanistan after a "sufficiently rigorous" review process.

Mattis did not provide details on when the White House would make an announcement or what the decision was on Afghanistan.

This comes after Trump’s administration began a review over US policy on Afghanistan soon after taking office in January.

"I am very comfortable that the strategic process was sufficiently rigorous and did not go in with a pre-set position," Mattis told reporters traveling with him aboard in a military aircraft to Jordan. "The president has made a decision. As he said, he wants to be the one to announce it to the American people."

On Friday, Trump met with his national security aides to review an array of options for the Afghan strategy but the White House said no decision had been made on whether he would commit more troops to America's longest war.

However, Trump after the meeting tweeted on Saturday: "Many decisions made, including on Afghanistan".

Quoted by Reuters, one US official, speaking on condition of anonymity, said Trump's top national security aides are backing adding between 3,000 and 5,000 troops and allowing them to embed with Afghan forces closer to combat, according to the report.