Russia may be supplying Taliban insurgents in Afghanistan, the top US commander in Europe has said.

Army General Curtis Scaparrotti, who is also Nato's Supreme Allied Commander in Europe, told a senate hearing he had seen Russian influence on Afghan Taliban insurgents growing.

"I've seen the influence of Russia of late — increased influence in terms of association and perhaps even supply to the Taliban," Mr Scaparotti said.

It comes after Taliban fighters captured the strategic district of Sangin in the southern Afghan province of Helmand after security forces pulled out, officials said.

Helmand, which accounts for the bulk of Afghanistan's billion dollar opium crop, is already largely in the hands of the Taliban but the capture of Sangin, where US and British forces once suffered heavy casualties, underlines their growing strength in the south.