America's top general in Afghanistan has said there was no doubt that Russia was providing weapons to the Taliban.
In the strongest statement yet over Russia's apparent re-engagement in the Afghanistan war, Gen John Nicholson said he would "not refute" that Moscow's involvement included giving weapons to the Taliban.
He was speaking in Kabul alongside James Mattis, the US defence secretary, who said that America needed to confront Russia over its actions in Afghanistan, where the Soviet Union fought and lost a bloody war in the 1980s.
"We'll engage with Russia diplomatically," Mr Mattis said. "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 any weapons being funneled here from a foreign country would be a violation of international law."
An unnamed US military official said that Russia was supplying machine guns and other medium-weight weapons to the Taliban.
The weapons were being used to attack Afghanistan’s security forces in the southern provinces of Helmand, Kandahar and Uruzgan, intelligence showed.
From 2006 onwards, British troops led a series of operations to control Helmand. It is where the vast majority of Britain's 454 casualties during the war occurred, but since the end of Nato combat operations in 2014, the Taliban has reasserted itself.
Russia denies that it provides any military support to the Taliban, and states contacts are limited to safeguarding security and getting the hard-line religious fundamentalists to reconcile with the government.
Mr Mattis was in the country to meet President Ashraf Ghani and other political and military leaders as the Trump administration aims to to craft a new Afghanistan strategy.
His visit came just days after the biggest ever insurgent assault on a military base in Afghanistan.
More than 140 Afghan troops were massacred on Friday when multiple gunmen and suicide bombers in army uniforms penetrated a military compound in northern Balkh province.
Abdullah Habibi, the Afghan defence minister, and a senior army chief resigned yesterday in the wake of the attack.
Mr Mattis said: "2017 is going to be another tough year for the valiant Afghan security forces and the international troops who have stood, and will continue to stand, shoulder to shoulder with Afghanistan against terrorism."
He branded the Taliban "barbaric", but would not be drawn on recent calls to send more troops to help battle the resurgent militants, who are gearing up for the spring fighting season.