WASHINGTON - The outgoing US top commander in Afghanistan has told a Congressional hearing that his troops were stepping up pressure against terrorist groups in the war-torn country, while Pakistan's military operations against extremists networks.

"I think Pakistan has done a lot of stuff in the last year," Gen John Campbell the commander told the House Armed Services Committee on Tuesday.

"Very courageously from General Raheel (Sharif), the Chief of Pakistani Army, to have military operations in Pakistan. But the result of that has driven a lot of that into Afghanistan and the Afghan forces have had to deal with that as well."

Lt Gen John W “Mick” Nicholson Jr would replace Gen. Campbell as the top US commander of US Forces in Afghanistan and NATO’s Resolute Support mission in March.

Gen. Campbell also said that the United States should retain an American troops presence in Afghanistan through the next five years to ensure Afghan security forces can effectively fight the Taliban and other insurgents.

He said that that Afghan leaders are “skeptical we will continue to be there” beyond the end of 2016.

In addition, Campbell said that President Barack Obama’s plan to draw down to 5,500 troops by the end of 2016 from the 9,800 service members in Afghanistan now, would leave the United States with “a very limited ability” to conduct its counter-terrorism operations and its mission to train, advise and assist Afghan security forces.

The 5,500 troops would focus primarily on targeting al Qaeda and Islamic State terrorists, he said.

Obama’s current plan leaves troops level decisions beyond the beginning of 2017 to the next President.

Campbell intends to retain 9,800 troops at least through the end of the summer fighting season and begin removing troops no later than October.

“The United States must continue to show flexibility with our mission in 2016 and beyond,” Campbell said during his testimony. “As the commander ... I’m assessing the ways that we ensure that 2016 is not a repeat of 2015 based on conditions and performance of Afghan security forces during this winter lull. I’m also reviewing how well those forces will likely perform in 2017 and the United States and coalition resources that are required for their development.”

Campbell said setbacks faced last year by the Afghan security forces in northern and southern Afghanistan were “disappointing.”

But he said that the Afghans quickly rebounded in their first year leading combat operations in their own country. Insurgents control or influence only 26 of 407 district centers in Afghanistan and the government controls 70 per cent of the country’s inhabited areas, Campbell said.

“The enemy and naysayers predicted the collapse of the Afghan government and security forces … instead the Afghan security forces fought for their country,” Campbell said. “They did not fall … They inflicted higher casualties on their enemy while enduring a higher operational tempo with significantly reduced coalition support.”

The vast majority of the failures of the Afghan National Security Forces in recent months – such as the short-lived loss of control of the City of Kunduz in October and the more recent struggles against the Taliban in Helmand province – were the result of poor leadership, Campbell said.

The Afghan Army has fired 92 general officers, which includes a commander in Helmand. The changes show the Afghanistan government’s commitment to its security, the General said.

“Now more than ever, the United States should not waiver on Afghanistan,” Campbell said. “…This kind of change takes time.”

The Afghans require American help in many areas including gathering intelligence, building its aviation programmes and developing the systems to construct and maintain an enduring military, he said.

But some lawmakers on Tuesday questioned America’s seemingly unending commitment to the nearly 15-year-old war in Afghanistan.