US National Security Adviser H.R. McMaster has defended President Donald Trump's military strategy in Afghanistan, after the president said the United States is “losing” in the war-torn country.

During a recent meeting with his national security team, Trump reportedly said, “We aren't winning," in Afghanistan. "We are losing."

According to reports, Trump wanted to fire Army General John Nicholson, commander of US forces in Afghanistan, over his failure to improve security situation in the country where the United States sent forces about 16 years ago to defeat the Taliban but the militant group is still fully operative.

But in a radio interview on Saturday, Trump’s national security adviser claimed the president "absolutely" has confidence in Nicholson.

"I’ve known him for many years," McMaster said of Nicholson. "I can’t imagine a more capable commander on any mission."

Trump makes 'a number of decisions' on Afghanistan

Haneef Atmar, national security adviser to the president of Afghanistan, welcomes Lt. Gen. H.R. McMaster, the US national security adviser, to talks in Kabul about the country’s security situation, Sunday, April 16, 2017.

McMaster said Trump he has made “a number of decisions" on the military approach in Afghanistan.

"The president’s already made some important decisions on Afghanistan," he said.

"And what we’re endeavoring to do is pull this all together in a regional strategy that makes sense," he continued.

Trump wants to see ‘change in behavior’ from certain countries

In addition, McMaster said that the Trump administration wants to see a "change in behavior" from certain countries in the region, particularly Pakistan.

"This is Pakistan in particular that we want to really see a change in– and a reduction of their support– for– these groups," he said. "I mean, this is– of course, you know, a very paradoxical situation, right, where Pakistan is taking great losses."

"They have fought very hard against these groups," McMaster argued, "but they’ve done so really only selectively."

He went on to say that President Trump is making clear that Washington will no longer tolerate any support for Taliban militants.

"The president has also made clear that he, that we need to see a change in behavior of those in the region, which includes those who are providing safe haven and support bases for the Taliban," McMaster added.

US Army General John Nicholson

General Nicholson has been the commander of US forces in Afghanistan since March 2016. Trump’s military advisers reportedly offered to arrange a meeting between the president and the general in order to help ease concerns, but Trump did not meet him.

In February, Nicholson was the first to call the war a stalemate and said that several thousand troops should be added to around 10,000 troops already stationed in the war-ravaged country to support the Afghan security forces against Taliban militants.

The United States -- under Republican George W. Bush’s presidency -- and its allies invaded Afghanistan on October 7, 2001 as part of Washington’s so-called war on terror.

Washington claims that the massive military presence in Afghanistan is only aimed at maintaining security across the country until Afghan military forces are ready to take over the responsibility.