The top US commander in Afghanistan said Thursday he needs a “few thousand” more troops to better accomplish an integral part of the mission, and he complained that Russian meddling is complicating the counter-terrorism fight.

Gen John Nicholson didn't provide the Senate Armed Services Committee with an exact number of additional forces, but said they could come from the United States or other countries in the American-led coalition in Afghanistan, where the war is now in its 16th year.

He said they are necessary to properly train and advise the Afghan military and perform work now handled at greater cost by contractors.

There are currently about 8,400 US troops conducting counter-terrorism operations against insurgents and training the Afghan army.

Nicholson said he had discussed troop levels with Defence Secretary Jim Mattis and Gen Joseph Dunford, chairman of the Joint Chiefs of Staff.

Nicholson said he believes the Trump administration will be open to a level based on requirements, rather than a predetermined figure.

Republicans criticised President Barack Obama for trying, in their view, to cut the number too sharply before he left office Jan, 20. But the idea of sending more Americans to the war zone may not go over well with a public frustrated by the length and cost of the conflict.

Senator Elizabeth Warren, citing figures from the special inspector general for Afghanistan reconstruction, said the war is costing US taxpayers $13 million a day.

Nicholson also disclosed that a US special forces soldier was “severely wounded” in fighting Thursday in Sangin, the Taliban heartland in southern Afghanistan.

He said that because of troop level limits, the aviation brigade that deployed to Afghanistan was able to bring its helicopters, pilots and staff, but had to leave its mechanics behind at Fort Riley in Kansas.

Contractors were hired instead at a cost of “tens of millions of dollars,” forcing the soldier mechanics to sit at home, he said, and affecting the Army unit's readiness.

Nicholson said there is a 2-1 ratio of contractors to troops in Afghanistan.

In response to a question from Sen Claire McCaskill, Nicholson said he doesn't have enough troops to provide proper oversight of all those contractors.

Nicholson contended that Russia has been publicly legitimising the Taliban by claiming that the militants are fighting terrorists while the Afghan government is not. He called that a “false narrative” and argued that Moscow's goal is to undermine the United States and NATO in Afghanistan.

Afghan security forces have reduced by one-half the number of IS fighters and by two-thirds the amount of territory the extremists hold, according to the commander. He said declined to say in the open hearing whether Russia is providing support for the Taliban and in what way.

The Russians recently invited representatives from the Taliban, China, Pakistan and other countries in the region to Moscow for meetings about Afghanistan's future, but did not include officials from the Kabul government, Nicholson said.

International Red Cross suspends activities in Afghanistan

The international Red Cross on Thursday temporarily suspended its activities in Afghanistan following an attack that killed six of its employees the previous day in a northern province.

According to Thomas Glass, spokesman for the International Committee of the Red Cross, the aid group's “activities are on hold” until next Tuesday or possibly longer.

The organisation, he told The Associated Press, needs “to reassess how we can conduct our work” safely following Wednesday's attack near the northern town of Shibirghan.

Glass described the assault as the “worst incident” for ICRC in 16 years in Afghanistan. The eight-person ICRC team was delivering livestock materials near Shibirghan, the capital of Jowzjan province, when the gunmen attacked their convoy.

“We are not planning to leave Afghanistan,” he added.

“We need to have a dialogue with all parties in the conflict about the security and safety of our staff.”

No one has claimed responsibility for the attack, but the provincial police chief, Rahmatullah Turkistani, said it was likely carried out by the militant Islamic State (IS) group, who have a presence in the area.

The Taliban, who have been waging a 15-year insurgency against the Kabul government, denied involvement.