The leader of US and international forces in Afghanistan has said that he is “not refuting” reports that Russia is providing weapons to the Taliban.

General John Nicholson made the comments to reporters in Kabul on Monday during US Defence Secretary Jim Mattis’s first trip to the country as part of US President Donald Trump’s administration.

While Gen. Nicholson did not provide details, he said he would not dispute claims made to media by an anonymous senior US military official in Kabul earlier that day that Russia had stepped up its assistance to insurgents over the last 18 months, providing machine guns and other medium weight weaponry to fighters in Helmand, Kandahar and Uruzgan.

Afghanistan: Fifteen years since US-led invasion

Russia has denied providing the Taliban - which ruled Afghanistan until the US invasion in 2001 - with any material or financial aid.

It says it maintains diplomatic ties with Taliban officials in order to push for peace negotiations with the Afghan government and to maintain security.

The US has called Russia’s presence in the country a “malign foreign influence.”

Moscow has long been critical of the US’ handling of its war in Afghanistan, and the years of failed efforts to bring peace.

The Soviet Union fought its own bloody war in the country in the 1980s, which ended in defeat. The CIA provided arms to Afghans resisting Soviet troops which analysts believe ended up falling into the hands of both the Taliban and al-Qaeda.

Afghanistan: Between Hope and Fear Show all 16 1 /16 Afghanistan: Between Hope and Fear Afghanistan: Between Hope and Fear 2001 Afghans at the Killi Faizo refugee camp desperately reach for bags of rice being handed out to the thousands who escaped the bombardment in southern Afghanistan during Operation Enduring Freedom. (Chaman, Pakistan, December 4, 2001) Paula Bronstein Afghanistan: Between Hope and Fear 2002 Mahbooba stands against a bullet-ridden wall, waiting to be seen at a medical clinic. The seven-year-old girl suffers from leishmaniasis, a parasitical infection. (Kabul, March 1, 2002) All photos Paula Bronstein Afghanistan: Between Hope and Fear 2003 A mother and her two children look out from their cave dwelling. Many families who, fleeing the Taliban, took refuge inside caves adjacent to Bamiyan’s destroyed ancient Buddha statues now have nowhere else to live. (Bamiyan, November 19, 2003) Paula Bronstein Afghanistan: Between Hope and Fear 2007 Students recite prayers in a makeshift outdoor classroom in the Wakhan Corridor, a mountainous region in northeastern Afghanistan that extends to China and separates Tajikistan from India and Pakistan. (Northeastern Afghanistan, September 2, 2007) Paula Bronstein Afghanistan: Between Hope and Fear 2007 Bodybuilders in the 55-60 kg category square off during a regional bodybuilding competition. Many Afghan men, like others around the world, feel that a macho image of physical strength is important. (Kabul, August 6, 2007) Paula Bronstein Afghanistan: Between Hope and Fear 2008 A woman in a white burqa enjoys an afternoon with her family feeding the white pigeons at the Blue Mosque. (Mazar-e-Sharif, March 8, 2008) Paula Bronstein Afghanistan: Between Hope and Fear 2009 Addicts inject heroin while trying to keep warm inside the abandoned Russian Cultural Center, which the capital city’s addicts use as a common gathering point. Heroin is readily available, costing about one dollar a hit. (Kabul, February 9, 2009) Paula Bronstein Afghanistan: Between Hope and Fear 2009 An elderly man holds his granddaughter in their tent at a refugee camp after they were forced to flee their village, which US and NATO forces had bombed because, they claimed, it was a Taliban hideout. (Surobi, Nangarhar Province, February 7, 2009) Paula Bronstein Afghanistan: Between Hope and Fear 2009 Seven-year-old Attiullah, a patient at Mirwais Hospital, stands alongside an X ray showing the bullet that entered his back, nearly killing him. Attiullah was shot by US forces when he was caught in a crossfire as he was herding sheep. (Kandahar, October 13, 2009). Paula Bronstein Afghanistan: Between Hope and Fear 2010 US Army Sargeant Jay Kenney (right), with Task Force Destiny, helps wounded Afghan National Army soldiers exit a Blackhawk helicopter after they have been rescued in an air mission. (Kandahar, December 12, 2010) Paula Bronstein Afghanistan: Between Hope and Fear 2010 An Afghan National Army battalion marches back to barracks at the Kabul Military Training Center. (Kabul, October 4, 2010) Paula Bronstein Afghanistan: Between Hope and Fear 2014 Eid Muhammad, seventy, lives in a house with a view overlooking the hills of Kabul. He and millions of other Afghans occupy land and housing without possessing formal deeds to them. (Kabul, November 21, 2014) Paula Bronstein Afghanistan: Between Hope and Fear 2014 Razima holds her two-year-old son, Malik, while waiting for medical attention at the Boost Hospital emergency room. (Lashkar Gah, Helmand Province, June 23, 2014) Paula Bronstein Afghanistan: Between Hope and Fear 2014 Young women cheer as they attend a rally for the Afghan presidential candidate Ashraf Ghani. (Kabul, April 1, 2014) Paula Bronstein Afghanistan: Between Hope and Fear 2014 Burqa-clad women wait to vote after a polling station runs out of ballots. (Kabul, April 5, 2014) Paula Bronstein Afghanistan: Between Hope and Fear 2015 Relatives, friends, and women’s rights activists grieve at the home of Farkhunda Malikzada, who was killed by a mob in the center of Kabul. Farkhunda was violently beaten and set on fire after a local cleric accused her of burning a Qur’an. (Kabul, March 22, 2015) Paula Bronstein

Monday's comments are among the strongest US suggestions yet that Moscow is providing arms to the Taliban.

The US must “confront” Russia on the issue, Secretary Mattis said.

“We’ll engage with Russia diplomatically… We’ll do so where we can, but we’re going to have to confront Russia where what they’re doing is contrary to international law or denying the sovereignty of other countries.”

“For example,” Mr Mattis told reporters, “any weapons being funnelled here from a foreign country would be a violation of international law.”

More than 140 Afghan troops were killed in a huge Taliban gunmen and suicide attack on a military base in Balkh province last week.

Referring to the massacre, Gen. Nicholson said that “anyone who arms belligerents who perpetuate attacks like the one we saw” isn’t focused on “the best way forward to a peaceful reconciliation.”

The US maintains around 9,800 troops in Afghanistan, mainly to support Afghan security forces. In recent comments to Congress Gen Nicholson said a “few more thousand” were necessary to make sure Afghan troops can eventually handle the Taliban insurgency on their own.

“2017 is going to be another tough year [in Afghanistan],” Mr Mattis said on Monday.