NATO is set to agree on Thursday to increase its Afghanistan training mission by some 3,000 troops, alliance officials said, after the United States switched tack in long-running efforts to defeat Taliban militants and end the conflict.

Fresh NATO personnel will not have a combat role but the alliance hopes more soldiers can train the Afghan army and air force to complement U.S. President Donald Trump's strategy to send more American counterterrorism troops to the country.

"We have decided to increase the number of troops ... to help the Afghans break the stalemate, to send a message to the Taliban, to the insurgents that they will not win on the battleground," NATO Secretary-General Jens Stoltenberg told a news conference on Tuesday.

NATO defence ministers are expected to approve the deployment in the latter part of a two-day meeting that starts on Wednesday. The troops would be deployed from the start of 2018, a NATO official said.

NATO secretary general Jens Stoltenberg speaks during a media conference at NATO headquarters in Brussels on Tuesday. (Virginia Mayo/Associated Press)

The NATO contribution would boost the training mission, called Resolute Support, to around 16,000 troops, Stoltenberg said.

About half the additional troops would come from the United States and the rest from NATO allies and partner countries.

Canada focusing on aid, training of security

U.S. Army General John Nicholson, the commander of the Resolute Support mission and of U.S. forces in Afghanistan, said in February that a few thousand more troops would make a difference. About 11,000 U.S. troops are serving in Afghanistan, the Pentagon said in August, including almost 7,000 in Resolute Support, according to NATO data.

Prime Minister Justin Trudeau said in the summer that Canada had "absolutely no plans to send any troops back to Afghanistan."

Canada formally ended its military mission in the country in 2014, two years later announcing $465 million would go to Afghanistan for the 2017-20 period, with about 60 per cent going towards development assistance and the rest for security support.

"We have served there with distinction, with valour, over 10 years and made a significant impact," Trudeau said in June, emphasizing the country's support for military and peacekeeping missions elsewhere in the world.

Global Affairs Canada recently confirmed to CBC News that there were no plans for Canada to change course and provide Resolute Support with more troops.

Stoltenberg hinted at an increase of about 3,000 in the summer and said at the time NATO had received commitments from up to 15 countries of its 28 member nations for the planned increase.

Trump's strategy in Afghanistan, unveiled in August, rests on providing more troops, a stronger Afghan army, support from regional allies such as India and a harder line with Pakistan. U.S. officials say Pakistan provides refuge and support to the Taliban and other extremist groups, which Pakistan denies.

Injured newsreader appears after station attack

Under Trump's new strategy, U.S. Defence Secretary Jim Mattis said in September that more than 3,000 additional U.S. troops would be deployed to Afghanistan.

Taken together, the new deployments could take the total number of Western troops in the country to above 20,000, according to current and projected troop numbers – well below a 2011 peak of more than 100,000.

Stoltenberg said an attack on Tuesday on a television station in Kabul underlined the importance of fighting militants and supporting Afghan security forces. Islamic State claimed responsibility for the assault, without giving evidence.

Afghan security officials take positions near the scene of an attack by armed men on Shamshad TV station in Kabul on Tuesday. (Hedayatullah Amid/EPA-EFE)

Police said at least two people were killed and 20 wounded.

"People dressed in police clothes came in and initially threw hand grenades, which killed one of our guards and wounded another," Abed Ehsas, Shamshad's news director told broadcaster Tolo News TV.

Some two hours later the station, which had replaced regular programmes with a still picture as the fighting went on, resumed normal service. Its newsreader appeared with a bandage on a hand from an injury apparently sustained in the attack.