WASHINGTON: Lieutenant General John Mick Nicholson, the current head of Nato's Allied Land Command, has been chosen as the new commander of international forces in Afghanistan, the Pentagon said on Wednesday amid concerns about setbacks in the fight against the Taliban.

Nicholson, whose selection must be confirmed by the Senate, would replace General John Campbell, who has commanded United States (US) and international forces in Afghanistan for the past 18 months and is expected to retire.

Nicholson is a veteran of multiple deployments in Afghanistan. He commanded the Army's 75th Ranger Regiment as well as the 82nd Airborne Division, Pentagon Press Secretary Peter Cook told a news briefing.

"He understands the importance and complexity of our mission in Afghanistan," Cook said, having served previously as chief of staff of operations for the International Security Assistance Force (ISAF) and US Forces Afghanistan.

The transition comes amid growing concern about the security situation in Afghanistan, where Taliban militants have caused large numbers of casualties among Afghan troops and the militant Islamic State (IS) group's affiliates have made some inroads.

The Taliban seized the northern city of Kunduz last year before being driven out by the Army. They also seized districts in Helmand province and threatened the provincial capital, Lashkar Gah.

Brigadier General Wilson Shoffner, a spokesman for the international mission in Afghanistan, said last week that Afghan security forces had "mixed results" in their first year of carrying out the fight against the Taliban on their own.

"Whenever they conducted deliberate, planned operations, they actually did fairly well," he said. "Where they had trouble and they didn't do so well was in response to crisis situations."

The security situation prompted President Barack Obama to announce in October that the US would maintain a force of about 9,800 troops in Afghanistan through most of 2016 instead of drawing down to an embassy-based presence by 2017.